Method of making silver-containing dispersions

ABSTRACT

A method is used to prepare silver nanoparticles or copper nanoparticles in the form of a silver nanoparticle cellulosic polymeric composite or a copper nanoparticle cellulose polymeric composite, respectively. A cellulosic polymer, organic solvent having a boiling point at atmospheric pressure of 100° C. to 500° C. and a Hansen parameter (δ T   Polymer ) equal to or greater than that of the cellulosic polymer, ascorbic acid, and a nitrogenous base are mixed to form a premix solution. At room temperature or upon heating the premix solution to a temperature of at least 40° C., a solution of reducible silver ions or reducible copper ions is added. The resulting silver or copper nanoparticle composite is cooled, isolated, and re-dispersed in an organic solvent, providing a non-aqueous silver-containing or copper-containing dispersion that can be disposed on a substrate to form an article.

RELATED APPLICATIONS

Reference is made to the following commonly assigned and copendingpatent application, the disclosures of all of which are incorporatedherein by reference:

U.S. Ser. No. 15/______ filed on even date herewith by Shukla) andentitled “Silver and Copper Nanoparticle Composites” (Attorney DocketK002222/JLT);

U.S. Ser. No. 15/456,686 filed Mar. 13, 2017 by Shukla and Donovan;

U.S. Ser. No. 15/456,827 filed Mar. 13, 2017 by Shukla, Donovan, andGillmor;

U.S. Ser. No. 15/456,868 filed Mar. 13, 2017 by Shukla and Donovan;

U.S. Ser. No. 15/713,773 filed Sep. 25, 2107 by Shukla and Donovan;

U.S. Ser. No. 15/713,777 filed Sep. 25, 2017 by Shukla, Donovan, andKlubek;

U.S. Ser. No. 15/713,786 filed Sep. 25, 2017 by Shukla and Donovan; and

U.S. Ser. No. 15/713,795 filed Sep. 25, 2017 by Shukla and Donovan.

FIELD OF THE INVENTION

This invention relates to a method for forming a non-aqueous dispersionof a silver nanoparticle composite by mixing a cellulosic polymer, ahydroxylic solvent, ascorbic acid, and a nitrogenous base, to whichreducible silver ions are introduced, to form a silver nanoparticlecomposite. After cooling and isolation, the silver nanoparticlecomposite can be re-dispersed in one or more organic solvents for use asan “ink” for forming a layer or pattern of silver nanoparticlecomposites on a substrate to provide an article having anelectrically-conductive layer or pattern.

BACKGROUND OF THE INVENTION

It is well known that silver has desirable electrical and thermalconductivity, catalytic properties, and antimicrobial behavior. Thus,silver and silver-containing compounds have been widely used in alloys,metal plating processes, electronic devices, imaging sciences, medicine,clothing or other fibrous materials, and other commercial and industrialarticles and processes to take advantage of silver's beneficialproperties.

For example, silver compounds or silver metal have been described foruse as metallic patterns or electrodes in metal wiring patterns, printedcircuit boards (PCBs), flexible printed circuit boards (FPCs), antennasfor radio frequency identification (RFID) tags, plasma display panels(PDPs), liquid crystal displays (LCDs), organic light emitting diodes(OLEDs), flexible displays, and organic thin film transistors (OTFTs),among other electronic devices known in the art.

Rapid advances are also occurring for making and using variouselectronic devices for communication, financial, and archival purposes.

Silver is an ideal conductor having electrical conductivity 50 to 100times greater than indium tin oxide that is commonly used today in manydevices. For example, the art has described the preparation ofelectrically-conductive films by forming and developing (reducing) asilver halide image in “photographic” silver halide emulsions through anappropriate mask to form electrically-conductive grid networks havingsilver wires having average sizes (width and height) of less than 10 μmand having appropriate lengths.

While silver as an electrical conductor has a wide range of potentialuses in the field of printed electronics, the microfabrication ofelectrically-conductive tracks (grids, wires, or patterns) byphotolithographic and electroless techniques is time consuming andexpensive, and there is an industrial need for direct digital printingto simplify the processes and to reduce manufacturing costs.

Furthermore, it is desirable to fabricate silver-containing electronicsonto polymeric or similar temperature-sensitive substrates bysolution-based printing processes. Metallic electrically-conductivewires or grids of low resistance must be achieved at sufficiently lowtemperatures to be compatible with organic electronics on polymericsubstrates. Among various known methods for fabricatingelectrically-conductive silver grids or patterns, the direct printing ofsilver-containing inks provides attractive prospects for making suchelectrically-conductive patterns.

Inkjet printing and flexographic printing have also been proposed forproviding patterns of silver or silver-containing compounds, requiringthe careful fabrication of a silver-containing paste or “ink” withdesirable surface tension, viscosity, stability, and other physicalproperties required for such application processes. High silver contenthas generally been required for high electrical conductivity, andcalcination or sintering may be additionally required for increasingelectrical conductivity of printed silver inks.

Some approaches to providing silver metal is to employ a chemical inkformulation where the silver source is a molecular precursor or cation(such as a silver salt) that is then chemically reacted (or reduced) toproduce silver metal. Electrically-conductive inks that are in the formof a chemical solution rather than as a suspension or dispersion ofmetal particles, have gained interest in recent years. One conductiveink of this type is known as a Metalorganic Decomposition (MOD) varietyink, for example, as described by Jahn et al. [Chem. Mater. 22,3067-3071 (2010)] who investigated silver printing using an aqueoustransition metal complex [AgO₂C(CH₂OCH₂)₃H]-containing MOD ink. Theyreported the formation of metallic silver features having electricalconductivities as high as 2.7×10⁷ S m⁻¹, which corresponds to anelectrical conductivity that is 43% of that of bulk silver, although asintering temperature of 250° C. was required.

U.S. Patent Application Publication 2015-0004325 (Walker et al.)describes a chemically-reactive silver ink composition comprised of acomplex of a silver carboxylate salt and an alkylamine, in which thecomplex is used to form an electrically-conductive silver structure at atemperature of 120° C. or less. Unfortunately, even these temperaturesrender the ink incompatible with many polymeric and paper substratesused in flexible electronic and biomedical devices. Furthermore, sincealkylamines are known to reduce silver at room temperature, long termstability of such compositions is tentative. Furthermore, thepublication teaches long heating times were needed to obtain lowresistivity in the resulting articles.

Other industrial approaches to preparing electrically-conductive filmsor elements have been directed to formulating and applying photocurablecompositions containing dispersions of metal particles such as silvermetal particles to substrates, followed by curing the photocurablecomponents in the photocurable compositions. The applied silverparticles in the cured compositions can act as catalytic (seed)particles for electrolessly plated electrically-conductive metals.Useful electrically-conductive grids prepared in this manner aredescribed for example, in U.S. Pat. No. 9,188,861 (Shukla et al.) andU.S. Pat. No. 9,207,533 (Shukla et al.) and in US Patent ApplicationPublications 2014/0071356 (Petcavich) and 2015/0125596 (Ramakrishnan etal.). Using these methods, photocurable compositions containingcatalytic silver particles can be printed and cured on a suitabletransparent substrate, for example, a continuous roll of a transparentpolyester film, and then electroless metal plating can be carried out onthe catalytic silver particles. However, these methods require that highquantities of purchased silver particles be uniformly dispersed withinthe photocurable compositions so that coatings or printed patterns havea sufficiently high concentration of catalytic sites. Without effectivedispersing, silver particles readily agglomerate, leading to lessineffective electroless plating and electrical conductivity.

Moreover, forming stable patterns of silver particles in this mannerrequires the presence of photosensitive components such as polymerizablemonomers or cross-linkable polymers that must be exposed to suitableradiation. Scaling such curing procedures to high volume use can bedifficult and hard to reproduce on a consistent scale, especially toproduce fine line electrically-conductive meshes or grids where theuniformity and size of fine lines are subjected to highly rigorousstandards.

Efforts are being directed in the industry to avoid the need forphotocuring. For, example, U.S. Patent Application Publication2012/0225126 (Geckeler et al.) describes a solid-state method forpreparing silver nanoparticles using a mixture of a silver salt and awater-soluble polymer such as a starch or cellulose derivative that actsas a silver ion reducing agent. The mixture is milled by a high-speedvibration milling process to form silver nanoparticles within thewater-soluble starch or cellulosic polymer so that a solvent is notneeded for synthesis or transportation of the silver nanoparticles.

Various methods have been employed in the production of silvernanoparticles, such as co-precipitation methods in an aqueous solution,electrochemical methods, aerosol methods, reverse microemulsion methods,chemical liquid deposition methods, photochemical reduction methods,chemical reduction methods in a solution and UV irradiation methods.However, the conventional technologies have difficulties in the controlof particle sizes and large-scale production of particles.

There are a variety of methods for producing nanometer-sized metallicnanoparticles. For example, U.S. Pat. No. 6,572,673 (Lee et al.)discloses a process for preparing metal nanoparticles, comprisingreacting suitable metal salts and anionic surfactant containing ananionic group such as a carboxylic group, sulfate group, or sulfonategroup as reducing agent in water under reflux at a temperature of50-140° C. Such processes are carried out in aqueous solutions.

U.S. Pat. No. 9,005,663 (Raghuraman et al.) discloses a method formaking silver nanoparticles, comprising reacting a silver salt with aphosphene amino acid. However, the phosphene amino acid reactant is anexpensive material.

U.S. Pat. No. 7,892,317 (Nia) discloses a process for the synthesis ofsilver nano particle, consisting of reacting silver salt and an anionicsurfactant, or a nonionic surfactant, and a reducing agent in an aqueoussolution at room temperature.

U.S. Pat. No. 9,496,068 (Kurihara et al.) discloses a process for thesynthesis of amine coated silver nano particles via thermaldecomposition of oxalate ion-alkylamine-alkyl diamine-silver complex.

U.S. Patent Application Publication 2010/0040863 (Li) discloses aprocess for producing carboxylic acid-stabilized silver nanoparticles byheating a mixture of a silver salt long alkyl chain carboxylic acid anda tertiary amine in methanol.

U. S. Patent Application Publication 2014/0312284 (Liu et al.) disclosesa process for producing an organoamine stabilized silver nanoparticle byreduction of silver salts with hydrazine in methanol. However, hydrazineis a toxic material and it would not be desirable to include it in amanufacturing process.

Cellulose is a polydisperse linear homopolymer consisting ofregioselective and enantioselective β-1,4-glycosidic linked D-glucoseunits. The homopolymer contains three reactive hydroxyl groups at theC-2, C-3 and C-6 atoms that are in general, accessible to the typicalchemical conversions of primary and secondary —OH groups.

The use of cellulose together with its derivatives has wide spreadapplications, for example in fibers, films, plastics, coatings,suspension agents, composites. With the advent of synthetic polymers,their uses have somewhat diminished, but cellulose derivatives are stillthe raw materials of choice for some uses. In addition, various studiesare on-going to look for and expand their use in existing and newtechnologies. Cellulosic polymers can be considered renewable resourcesin some instances. An inherent problem that faces users of cellulosicpolymers is their general insolubility in most common solvents.Modifying the structure of cellulosic polymers can improve theirsolubility, leading to the synthesis of various cellulose derivatives(cellulosics) that come in all forms and structures depending on thefunctional group(s) used in place of the hydroxyl groups on thecellulose chain.

For example, cellulose derivatization can involve partial or fullesterification or etherification of the hydroxyl groups on the cellulosechain by reaction with various reagents to afford cellulose derivativeslike cellulose esters and cellulose ethers. Among all cellulosederivatives, cellulose acetate is recognized as the most importantorganic ester of cellulose owing to its extensive industrial andcommercial importance. Properties of cellulose derivatives (esters andethers) are determined primarily by the functional group. However, theycan be modified significantly by adjusting the degree offunctionalization and the degree of polymerization of the polymerbackbone to modify solubility in various solvents.

The solution properties of cellulose acetates have been well studied andhave been shown to be influenced by the average degree of substitutionand the distribution of substituents along the chain. Previous work onthe gelation mechanism of cellulose acetate has shown interestingbehavior with respect to the sol-gel transition. Cellulose acetate gelsexhibit thermally reversible properties that depend on factors such asconcentration, acetyl content, and the type of solvent. It is usuallydifficult to predict if cellulose will gel in a given organic solvent,and in most cellulose acetate/solvent systems, gelation occurs after thesolution is heated to a specific temperature and subsequently cooled.For example, Kwon et al., Bull. Korean Chem. Soc. 26(5), 837-840describe a study of silver nanoparticles in cellulose acetate solutions.

U.S. Ser. No. 15/456,686 (noted above) describes a method for preparingarticles using silver nanoparticles that are obtained by thermalreduction of reducible silver ions in the presence of certain cellulosicpolymers.

Besides silver particles, copper particles (including nanoparticles andmicroparticles) and gold particles (including nanoparticles andmicroparticles) are the most significant metallic particles that havefound wide application, especially in electronics and catalysis, due totheir excellent electrical conductivity, catalytic abilities, and highchemical stability. As for silver, several different methods have beendevised for the preparation of copper particles having dimensions in therange of from tens of nanometers to micrometers, some of the methodsbeing more suitable that others. However, apart from indisputablebenefits, the methods that are currently used also exhibit severaldisadvantages.

The most widely used methods for preparation of copper particles arebased on liquid-step reduction, in which metallic copper is produced byreduction from a suitable precursor dissolved in a suitable solvent byusing a suitable reducing agent. The mean size of the particles thusprepared depends on the ratio of the copper precursor to the reducingagent, as well as on the specific reaction conditions (for example,temperature, stirring conditions, order of mixing individual componentstogether, and addition of other reagents). The most commonly used copperprecursors are copper sulfate, copper chloride, copper nitrate, copperacetylacetonate, copper acetate, cuprous oxide, and cupric oxide. Fordissolution of these copper precursors, different solvent systems areused, most often on the basis of water, organic solvents (such asacetone or toluene), alkanes (such as n-hexane, n-heptane, andn-octane), ethylene glycol, polyethylene glycols, or various mixturesthereof. As a reducing agent especially sodium borohydrate (NaBH₄) orpotassium borohydrate (KBH₄) is used [see, for example Lisiecki et al.,Journal of the Physical Chemistry 100 (1996) 4160, or Zhang et al.,Nanoscale Research Letters 4 (2009) 705] as well as hydrazine [see, forexample, Wu et al., Journal of Colloidal Interface Science 273 (2004)165], sodium hypophosphite [see, for example, Lee et al., Nanotechnology19 (2008) 415604], and ascorbic acid in an alcohol-water mixture [see,for example, Yu et al., Nanoscale Research Letters 4 (2009) 465].

U.S. Patent Application Publication 2012/0251381 (Bedworth et al.)discloses a method for preparation of copper particles by usingliquid-step reduction.

U.S. Patent Application Publication 2008/0159902 (Shim et al.) describesthe preparation of copper particles having a diameter below 100 nm by asequence of dispersion of Cu₂0 or CuO microparticles in a hot solutionof an amine compound and subsequent chemical reduction in a mixture ofoleic acid and formic acid.

WO 2009-040479 (Maijala et al.) discloses the preparation of coppernanoparticles with a diameter ranging from 1 nm to 10 nm using copperchloride and NaBH₄ in an ethanol-chloroform solution.

The disadvantage of all these methods is that they require long reactiontimes, a great excess of the reducing agents, high temperatures andpressures and, above all, the use of exotic and often highly toxicsubstances, which makes these methods difficult to be scaled up and usedin an industrial environment. Moreover, the final price of the producedcopper particles can be negatively influenced to a considerable extentby a potential use of other additives, such as surfactants (for betterwetting of the produced particles), particle stabilizers, and othernecessary process additives. Another drawback is the necessity to use ahighly expensive process of bubbling inert gases through a reactionmixture in order to avoid undesirable oxidation of the produced copperparticles.

Therefore, there is a need to eliminate the disadvantages of the knownprocesses for producing either silver or copper nanoparticles. Despiteall the various approaches and efforts to provideelectrically-conductive silver or copper in various consumer andindustrial articles, there remains a need for simpler and less expensivecompositions and methods for generation of silver nanoparticles in afashion suitable particularly for pattern formation in high speedmanufacturing processes at low temperature using minimally toxic organicsolvents.

SUMMARY OF THE INVENTION

The present invention provides a method comprising, in sequence:

1. A method comprising, in sequence:

A) mixing:

(a) one or more polymers selected from one or more of cellulose acetate,cellulose acetate phthalate, cellulose acetate butyrate, celluloseacetate propionate, cellulose acetate trimellitate, hydroxypropylmethylcellulose phthalate, methyl cellulose, ethyl cellulose, hydroxyethylcellulose, hydroxypropylmethyl cellulose, and carboxymethyl cellulose;

(c) one or more organic solvents, each of which has a boiling point atatmospheric pressure of greater than or equal to 90° C. and up to butless than 500° C., wherein the total Hansen parameter (δ_(T) ^(Polymer))of each of the one or more polymers is less than or equal to the totalHansen parameter (δ_(T) ^(Solvent)) of each of the one or more organicsolvents;

(d) a nitrogenous base having a pKa in acetonitrile of at least 15 andup to and including 25 at 25° C.; and

(e) ascorbic acid,

to form a premix solution;

B) maintaining the premix solution at room temperature or heating thepremix solution to a temperature of at least 40° C.;

C) while keeping the premix solution at room temperature or at thetemperature of at least 40° C., adding a solution of either (b)reducible silver ions or (b′) reducible copper ions, in one or more (c)organic solvents to provide an amount of the (b) reducible silver ionsor (b′) reducible copper ions, respectively, in the premix solution thatis equimolar or less in relation to the (d) nitrogenous base, and aweight ratio of the (b) reducible silver ions or (b′) reducible copperions to the (a) one or more polymers of at least 5:1 and up to andincluding 50:1,

to form either a silver nanoparticle composite or a copper nanoparticlecomposite, respectively;

wherein the (e) ascorbic acid is provided in a molar amount of at least0.01:1 relative to either the (b) reducible silver ions or (b′)reducible copper ions, respectively, and

the (d) nitrogenous base is provided in a molar amount of at least 1:1to and including 3:1 relative either the (b) reducible silver ions or(b′) reducible copper ions, respectively,

D) after cooling, isolating the silver nanoparticle composite or thecopper nanoparticle composite; and

E) re-dispersing the silver nanoparticle composite or the coppernanoparticle composite in the same or different (c) one or more organicsolvents used in A), to provide either a non-aqueous silver-containingdispersion or a non-aqueous copper-containing dispersion, comprising thesilver nanoparticle composite or the copper nanoparticle composite,respectively.

In some embodiments, this method further comprises:

disposing either the non-aqueous silver-containing dispersion or thenon-aqueous copper-containing dispersion onto a substrate to form asilver nanoparticle composite composition or copper nanoparticlecomposite composition, respectively, and

removing the same or different (c) one or more organic solvents.

In addition, the present invention provides an article provided by someembodiments of the method of the present invention, wherein either thesilver nanoparticle composite composition or the copper nanoparticlecomposite composition, is disposed in dry form on a first supportingside of the substrate, wherein:

the silver nanoparticle composite composition comprises silvernanoparticles, and both the (a) one or more polymers and ascorbic acidadsorbed on the silver nanoparticles; and

the copper nanoparticle composite composition comprises coppernanoparticles, and both the (a) one or more polymers and ascorbic acidadsorbed on the copper nanoparticles.

Thus, the present invention provides an industrially attractive meansfor preparing either copper particles or silver particles having asuitable size distribution in size in non-aqueous media at lowtemperatures. It is another object also to ensure protection of theprepared copper particles from undesired surface oxidation by a layer ofmaterial that is already present within the copper nanoparticlecomposite that is formed during the practice of the method.

The present invention provides a simple, safe, and inexpensive way togenerate a non-aqueous dispersion of silver nanoparticles or coppernanoparticles from a non-aqueous silver precursor composition ornon-aqueous copper precursor composition, respectively, comprisingreducible silver ions or reducible copper ions, respectively, acellulosic polymer, ascorbic acid, and a nitrogenous base. The methodaccording to this invention can be readily and safely carried out formanufacturing high weight fraction, fully dispersed silvernanoparticles, or copper nanoparticles, that have long term stability asthe respective nanoparticles do not readily agglomerate in therelatively benign organic solvents. These silver nanoparticle-containingcompositions or copper nanoparticle-containing compositions can beeasily deposited or formed into patterns for various uses. It is alsopossible to produce these compositions at relatively low temperatures,including room temperature.

The present invention provides these advantages by means of using acombination of ascorbic acid and a nitrogenous base to facilitate fastersilver ion or copper ion reduction in the presence of the cellulosicpolymer. The cellulosic polymers and organic solvents used in thenon-aqueous silver precursor compositions and non-aqueous copperprecursor compositions also facilitate silver or copper ion reductionand provide physical stability of the resulting silver nanoparticles orcopper nanoparticles using inexpensive and environmentally safedispersing agents. The inventive compositions and methods can thus beused to provide compositions or dispersions of silver nanoparticles orcopper nanoparticles that can be used in various ways, for example, asapplied to a substrate in a pattern for further processing.

Other advantages of the present invention would be readily apparent toone skilled in the art in view of the teaching provided herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphical representation of silver nanoparticle ethylcellulose composite particle size distribution as described below inInvention Example 1.

FIG. 2 is a black-and-white image of an electrically-conductive silverpattern provided according to Invention Example 2 described below.

FIG. 3 is a graphical representation of copper nanoparticle celluloseacetate composite particle size distribution as described below inInvention Example 3.

FIG. 4 is a graphical representation of X-ray diffraction analysis ofcopper nanoparticle cellulose acetate particles as described below inInvention Example 3.

FIGS. 5-7 represent data obtained in carrying out and evaluatingInvention Example 4 described below.

DETAILED DESCRIPTION OF THE INVENTION

The following discussion is directed to various embodiments of thepresent invention and while some embodiments can be desirable forspecific uses, the disclosed embodiments should not be interpreted orotherwise considered be limit the scope of the present invention, asclaimed below. In addition, one skilled in the art will understand thatthe following disclosure has broader application than is explicitlydescribed and the discussion of any embodiment.

Definitions

As used herein to define various components of the non-aqueous silverprecursor composition or non-aqueous copper precursor composition,unless otherwise indicated, the singular forms “a,” “an,” and “the” areintended to include one or more of the components (that is, includingplurality referents).

Each term that is not explicitly defined in the present application isto be understood to have a meaning that is commonly accepted by thoseskilled in the art. If the construction of a term would render itmeaningless or essentially meaningless in its context, the termdefinition should be taken from a standard dictionary.

The use of numerical values in the various ranges specified herein,unless otherwise expressly indicated otherwise, are approximations asthough the minimum and maximum values within the stated ranges were bothpreceded by the word “about.” In this manner, slight variations aboveand below the stated ranges can be used to achieve substantially thesame results as the values within the ranges. In addition, thedisclosure of these ranges is intended as a continuous range includingevery value between the minimum and maximum values.

Unless otherwise indicated, the term “weight %” refers to the amount ofa component or material based on the total amount of a non-aqueoussilver precursor composition or non-aqueous dispersion. In otherembodiments, “weight %” can refer to the % solids (or dry weight) of adry layer, coating, thin film, or silver-containing pattern.

Unless otherwise indicated, the term “non-aqueous” as applied to thecompositions and dispersions according to the present invention meansthat solvent media used to form such compositions are predominantlyorganic in nature and water is not purposely added but may be present inan amount of less than 10 weight % by virtue of being part of a chemicalcomponent, or particularly less than 5 weight %, or even less than 1weight %, of the total weight of all solvents in the composition.

Unless otherwise indicated, the term “non-aqueous silver precursorcomposition” means that the silver present therein is predominantly(greater than 50 weight % of total silver) in the form of reduciblesilver ions.

Unless otherwise indicated, the term “non-aqueous copper precursorcomposition” means that the copper present therein is predominantly(greater than 50 weight % of total copper) in the form of reduciblecopper ions.

The average dry thickness of silver nanoparticle-containing lines orcopper nanoparticle-containing lines, grid lines, or other patternfeatures described herein can be the average of at least 2 separatemeasurements taken, for example, using electron microscopy, opticalmicroscopy, or profilometry all of which should provide substantiallythe same results for the same test sample.

The use of “dry” in reference to thickness and width of lines, patterns,or layers, refers to embodiments in which at least 80 weight % oforiginally present organic solvent(s) has been removed.

As used herein for defining silver nanoparticles or coppernanoparticles, “mean particle size” is measured using dynamic lightscattering (DLS), that is sometimes referred to as Quasi-Elastic LightScattering (QELS), and is a well-established technique for measuring thesize and size distribution of molecules and particles typically in thesubmicron region, and even lower than 1 nm. Commercial DLS instrumentsare available from, for example, Malvern and Horiba who also supplyinstructions for use of such equipment, and such equipment and accompanyinstructions can be used to characterize and carry out the presentinvention.

The boiling point of organic solvents described herein can be determinedfrom known publications or measured using standard methods.

Unless otherwise indicated herein, viscosity can be determined at 25° C.using any standard commercially available viscometer.

Unless otherwise indicated, the term “group” particularly when used todefine a substituent or a moiety, can itself be substituted orunsubstituted (for example an “alkyl group” refers to a substituted orunsubstituted alkyl group) by replacement of one or more hydrogen atomswith suitable substituents (noted below) such as a fluorine atom.Generally, unless otherwise specifically stated, substituents on any“groups” referenced herein or where something is stated to be possiblysubstituted, include the possibility of any groups, whether substitutedor unsubstituted, which do not destroy properties necessary for theutility of the component or non-aqueous silver precursor composition ornon-aqueous copper precursor composition. It will also be understood forthis disclosure and claims that reference to a compound or complex of ageneral structure includes those compounds of other more specificformula that fall within the general structural definition. Examples ofsubstituents on any of the mentioned groups can include knownsubstituents such as halogen (for example, chloro and fluoro); alkoxy,particularly those with 1 to 5 carbon atoms (for example, methoxy andethoxy); substituted or unsubstituted alkyl groups, particularly loweralkyl groups (for example, methyl and trifluoromethyl), particularlyeither of those having 1 to 6 carbon atoms (for example, methyl, ethyl,and t-butyl); and other substituents that would be readily apparent inthe art.

Unless otherwise indicated, the terms “total Hansen solubilityparameter” and “total Hansen parameter” refer to the same thing. HansenSolubility Parameters (also named reverse solvency principle) weredeveloped by Charles Hansen as a way of predicting if one material willdissolve in another and form a solution. They are based on the conceptthat “like dissolves like” where one molecule is defined as being “like”another if it bonds to itself in a similar way. Each chemical moleculeis given three Hansen parameters, each generally measured inMpa^(0.5):δ_(d). the energy from dispersion bonds between molecules:δ_(p), the energy from polar bonds between molecules: and δ_(h), theenergy from hydrogen bonds between molecules. The “total Hansensolubility parameter” is defined as:

δ²=δ_(d) ²+δ_(p) ²+δ_(h) ²

These three Hansen parameters can be treated as co-ordinates for a pointin three dimensions also known as the Hansen space. The nearer that twomolecules are in this three dimensional space, the more likely they areto dissolve into each other. To determine if the total Hansen parametersof two molecules (usually a solvent and a polymer) are within range. avalue called the interaction radius (R₀) is given to the substance beingdissolved. This interaction radius determines the radius of the spherein the Hansen space and its center is the three Hansen parameters. Inorder to calculate the distance (Ra) between the Hansen parameters inthe Hansen space the following formula is used:

R _(a) ²=4(δ_(d1)−δ_(d2))²+(δ_(p1)−δ_(p2))²+(δ_(h1)−δ_(h2))²

The concept of a total Hansen parameter is well understood by anyoneskilled in the art. A detailed description of the derivation and theoryis found in various references such as (1) A. F. M. Barton, “Handbook ofPolymer-Liquid Interaction Parameters and Solubility Parameters,” CRCPress Inc. (1990) and (2) Solubility Parameter Values, Eric A. Grulke,Polymer Handbook, John Wiley and Sons, Inc. (1989). In many instances,the total Hansen parameter of each useful polymer can be obtained fromproduct literature where available, estimated from studies of similarmaterials as published in the Handbook of Polymer-Liquid InteractionParameters and Solubility Parameters, by Allan F. M. Barton, CRC Press(1990), or determined by solubility studies. The total Hansen parametersof organic solvent mixtures can be calculated using the sum of volumefractions of the individual organic solvent components in the premixsolution. Total Hansen parameters as well as the three-component Hansenparameters for dispersive, polar, and hydrogen-bonding components of thesolubility parameter, are readily available in the literature.

Uses

The deposition or patterning of functional electrodes, pixel pads, andconductive traces, lines, and tracks, that meets electricalconductivity, processing, and cost requirements for practicalapplications has been a great challenge. Silver metal and copper metalare of interest in the preparation of electrically-conductive elementsfor use in electronic devices with or without further electrolessplating.

The non-aqueous silver-containing dispersions described herein can beused for forming metallic silver patterns and electrodes, or metalliccopper patterns and electrodes, for example in membrane touch switches(MTS), battery testers, biomedical, electroluminescent lamps, radiofrequency identification (RFID) antenna, flat panel displays such asplasma display panel (PDP) and organic light emitting diode (OLED)displays, printed transistors and thin film photovoltaics, and therebyreduce the number of steps for pattern formation in such devices.

The non-aqueous silver precursor compositions and non-aqueous copperprecursor compositions described herein have actual and potential usesin various technologies and industries. Most specifically, they can beused to provide silver metal or copper metal, respectively, for variouspurposes, including but not limited to, the formation ofelectrically-conductive grids or patterns of fine wires or othergeometric forms, the formation of silver or copper seed particles forelectroless plating with other electrically-conductive metals, and theformation of silver in various materials for antimicrobial activity.

More specifically, the non-aqueous silver precursor compositions andnon-aqueous copper precursor compositions according to the presentinvention are useful to provide silver metal or copper metal innon-aqueous dispersions that in turn can be used to provideelectrically-conductive metal patterns. These electrically-conductivemetal patterns can be incorporated into various devices including butnot limited to, touch screens or other transparent display devices, andin modern electronics such as solar cell electrodes, electrodes inorganic thin film transistors (OTFTs), flexible displays, radiofrequency identification tags, light antennas, and other devices thatwould be readily apparent to one skilled in the art.

Non-Aqueous Silver Precursor Compositions

For all embodiments, the non-aqueous silver precursor compositionsaccording to the present invention contain five essential components forpurposes of providing silver metal in the form of silver nanoparticlesaccording to the present invention: one or more (a) polymers (such asone or more cellulosic polymers) as described below; (b) reduciblesilver ions in the form of one or more silver salts or silver complexesas described below; an organic solvent medium consisting of (c) or moreorganic solvents, as described below; (d) one or more nitrogenous bases,as described below; and (e) ascorbic acid as described below. No othercomponents are purposely added to the non-aqueous silver precursorcompositions according to the present invention in order to achieve theinventive advantages or purposes, and as noted above, water is notpurposely included. As described below, for some embodiments, (f) carbonblack can be present as a sixth essential component.

Upon thermal treatment, as described below, the non-aqueous silverprecursor composition according to this invention can be converted intoa corresponding non-aqueous dispersion or non-aqueous silver-containingdispersion comprising a silver nanoparticle composite comprising bothsilver and one or more polymers as described below. It is desirable thatat least 90 mol %, at least 95 mol %, or even at least 98 mol % (whichmeans “substantially all”) of the (b) reducible silver ions areconverted to silver during this process.

The one or more (a) polymers, (b) reducible silver ions, (c) organicsolvents, (d) nitrogenous bases, and (e) ascorbic acid can be combinedin general by mixing them under suitable ambient conditions so thatthermal reduction does not occur prematurely to any appreciable extent.In general, the (a), (c), (d), and (e) components can be formulated ormixed to form a premix solution and at room temperature or underappropriate heating, the (b) reducible silver ions can be added to thepremix solution in a controlled fashion. Details of this method aredescribed below.

Ultimately, the non-aqueous silver precursor composition is formed, andit generally has at least 1% solids and up to and including 70% solids,or more typically of at least 5% solids and up to and including 25%solids. The amount of solids, and (c) organic solvents, and viscosity,can thus be adjusted for a particular use or silver ion reductionoperation.

The non-aqueous silver precursor composition is generally in liquid formhaving a viscosity of at least 1 centipoise (0.001 Pascal sec) and up toand including 5,000 centipoise (5 Pascal sec), or more likely aviscosity of at least 3 centipoise (0.003 Pascal sec) and up to andincluding 50 centipoise (0.05 Pascal sec), all measured at 25° C.

The non-aqueous (silver-containing) dispersion described below can havethe same or different viscosity as the corresponding non-aqueous silverprecursor composition. In most embodiments, the two compositions haveessentially the same viscosity, that is, no more than 10% difference.

(a) Polymers:

The polymers useful in the practice of the present invention are organicin nature and can be used singly or in mixtures of two or more differentmaterials. When used in mixtures, the two or more different materialscan be present in the same or different amounts within the total polymeramount. Both cellulose esters and cellulose ethers can be used in thepresent invention.

Representative useful polymers for the practice of the present inventionare selected from cellulose acetate, cellulose acetate phthalate,cellulose acetate butyrate, cellulose acetate propionate, celluloseacetate trimellitate, hydroxypropylmethyl cellulose phthalate, methylcellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropylmethylcellulose, carboxymethyl cellulose, and mixtures of two or more of suchmaterials.

Particularly useful polymers according to the present invention includecarboxymethyl cellulose, cellulose acetate butyrate, cellulose acetatepropionate, ethyl cellulose, and cellulose acetate, individually or inmixtures.

It can also be useful to use cellulosic polymers such as celluloseesters that comprise free hydroxy groups directly attached to thepolymer backbone to provide a free hydroxyl content in an amount of atleast 1%, or at least 2%, and up to and including 5%, based on the totalhydroxy groups that could potentially be present in the polymer. Theremaining hydroxy groups in the molecule would be esterified so thatthere is relatively low free hydroxyl content.

The one or more (a) polymers can be present in a total amount of atleast 1 weight % and up to and including 25 weight %, or more likely ofat least 3 weight % and up to and including 10 weight %, based on thetotal weight of silver in the non-aqueous silver precursor composition.

Each of the useful polymers can be readily obtained from variouscommercial sources, or in some cases, they can be prepared using knownstarting materials, reaction conditions, and known synthetic procedures.

(b) Reducible Silver Ions:

Reducible silver ions can be provided in the non-aqueous silverprecursor composition from many sources as long as each silver salt orsilver complex in which they are provided is soluble within the one ormore (c) hydroxylic organic solvents at an amount of at least 1 g/literat 20° C. In general, silver salts or silver complexes comprised ofreducible silver ions and any suitable organic or inorganic anion orcomplexed moiety (or a combination of anions and complexed moieties) canbe used in the practice of the present invention to provide the (b)reducible silver ions for the present invention. Such silver complexescan be mononuclear, dinuclear, trinuclear, or higher and each compoundgenerally has a net neutral charge. The following classes of usefulreducible silver ion-containing salts and reducible silverion-containing complexes are described as representative materials, butthe present invention is not to be interpreted to be limited to them.Such reducible silver ion-containing materials can be readily purchasedfrom various commercial sources or prepared using known procedures,starting materials, and reaction conditions unless otherwise indicated.

(i) A first class of reducible silver ion-containing compounds aresilver salts having organic or inorganic anions. Some representativesilver salts include but not limited to, silver nitrate, silver acetate,silver benzoate, silver nitrite, silver thiocyanate, silver myristate,silver citrate, silver phenylacetate, silver malonate, silver succinate,silver adipate, silver phosphate, silver perchlorate, silveracetylacetonate, silver lactate, silver salicylate, silver oxalate,silver 2-phenylpyridine, silver trifluoroacetate; silver fluoride andsilver fluoride complexes such as silver (I) fluorosulfate, silver (I)trifluoromethane sulfate, silver (I) pentafluoropropionate, and silver(I) heptafluorobutyrate; β-carbonyl ketone silver (I) complexes; silverproteins; and derivatives of any of these materials.

(ii) Complexes of hindered aromatic N-heterocycle with (b) reduciblesilver ions can be used in the practice of this invention. The term“hindered” as used to define hindered aromatic N-heterocycle means thatthe moiety has a “bulky” group located in the α position to the nitrogenatom in the aromatic ring. Such bulky groups can be defined using theknown “A-value” parameter that is a numerical value used for thedetermination of the most stable orientation of atoms in a molecule(using conformational analysis) as well as a general representation ofsteric bulk. A-values are derived from energy measurements of amono-substituted cyclohexane ring. Substituents on a cyclohexane ringprefer to reside in the equatorial position to the axial. In the presentinvention, the useful “bulky” groups in the hindered aromaticN-heterocycle have an A-value of at least 0.05. Useful reducible silverion-containing complexes of this type are described in U.S. Pat. No.9,377,688 (Shukla), the disclosure of which is incorporated herein byreference for a further description of properties, representativecompounds, and methods for preparing them.

(iii) Other useful complexes comprise (b) reducible silver ions aresilver carboxylate-trialkyl, carboxylate-triaryl, andcarboxylate-alkylaryl phosphite complexes and mixtures of thesecompounds. The terms “carboxylate-trialkyl phosphite” and“carboxylate-triaryl phosphite” are to be interpreted herein asindicating that the complex of which it is a part can have three of thesame or different alkyl groups, or three of the same or different arylgroups, respectively. The term “carboxylate-alkylaryl phosphite” refersto a compound having a mixture of a total of three alkyl and arylgroups, in any combination. Useful reducible silver ion-containingcomplexes of this type are described in U.S. Pat. No. 9,375,704(Shukla), the disclosure of which is incorporated herein by referencefor a further description of properties, representative compounds, andmethods for preparing them.

(iv) Silver-oxime complexes can be used to provide (b) reducible silverions, and these materials are generally non-polymeric in nature (meaningthat the silver complex molecular weight is less than 3,000). Usefulnon-polymeric silver-oxime complexes of this type are described in U.S.Pat. No. 9,387,460 (Shukla), the disclosure of which is incorporatedherein by reference for a further description of properties,representative compounds, and methods for preparing them.

(v) Other useful silver complexes comprising (b) reducible silver ionscan be represented by the following Structure (I):

(Ag⁺)_(a)(L)_(b)(P)_(c)  (I)

wherein L represents an α-oxy carboxylate; P represents a 5- or6-membered N-heteroaromatic compound; a is 1 or 2; b is 1 or 2; and c is1, 2, 3, or 4, provided that when a is 1, b is 1, and when a is 2, b is2.

Each of the complexes of Structure (I) comprises one or two reduciblesilver ions. Each reducible silver ion is complexed with one or twoα-oxy carboxylate compounds that can be via two oxygen atoms providedfrom the same molecule of an α-oxy carboxylate compound, or oxygen atomsprovided from two molecules of the same or different α-oxy carboxylatecompounds.

The α-oxy carboxylate groups (moieties or components) can be defined inwhich the α-carbon atom attached directly to the carboxyl group[—C(═O)O-] has a hydroxy group, oxy, or an oxyalkyl substituent group.Thus, the α-oxy carboxylates can be either α-hydroxy carboxylates,α-alkoxy carboxylates, or α-oxy carboxylates. With the α-hydroxycarboxylates and α-alkoxy carboxylates, the remainder of the valences ofthat α-carbon atom can be filled with hydrogen or a branched or linearalkyl group (substituted or unsubstituted) as described below in moredetail. In addition, the α-oxy carboxylate (L) generally has a molecularweight of 250 or less, or 150 or less.

In Structure (I) shown above, b is 1 or 2, and in the embodiments whereb is 2, the two α-oxy carboxylate compounds within a single complexmolecule can be the same or different compounds. In some embodiments ofthe present invention, L of Structure (I) described above can berepresented by the following Structure (H):

wherein R₁, R₂, and R₃ are independently hydrogen or branched or linearalkyl groups. In most embodiments, at least one of R₁ through R₃ is abranched or linear alkyl group having from 1 to 8 carbon atoms, and anyof the hydrogen atoms in such branched or linear alkyl groups can bereplaced with a heteroatom such as a fluorine atom substituent.

Some particularly useful conjugate acids from which α-oxy carboxylates(L) of Structure (II) can be selected from the group consisting oflactic acid, 2-hydroxybutyric acid, 2-hydroxy-3-methylbutyric acid,2-hydroxy-3,3-dimethylbutyric acid, 2-hydroxy-isobutyric acid,2-hydroxy-2-methylbutyric acid, 2-ethyl-2-hydroxybutyric acid,2-hydroxy-2,3-dimethylbutyric acid, 2-ethyl-2-methoxybutyric acid,2-methoxy-2-methylpropanoic acid, 1-hydroxycyclopentane-1-carboxylicacid, 2,3-dihydroxy-2,3-dimethylsuccinic acid, and2,4-dihydroxy-2,4-dimethylpentanedioic acid. As noted above, mixtures ofthese materials can be used in a specific complex if desired.

In other embodiments, L is represented in Structure (I) by the followingStructure (III):

wherein R₄ is a branched or linear alkyl group having 1 to 8 carbonatoms, including branched iso- and tertiary alkyl groups having 3 to 8carbon atoms. In addition, any of the hydrogen atoms in any of thebranched or linear alkyl groups optionally can be replaced with afluorine atom; for example, the terminal carbon atom of a R₄ branched orlinear alkyl group can have 1 to 3 fluorine atoms.

Some useful conjugate acids from which the α-oxy carboxylate (L)represented by Structure (III) can be selected from the group consistingof pyruvic acid, 3-methylpyruvic acid, 3,3-dimethylpyruvic acid,3,3-dimethyl-2-oxobutanoic acid, 3,3-dimethyl-2-oxopentanoic acid, and2,3-dioxosuccinic acid.

The “P” compound of Structure (I) is a 5- or 6-membered N-heteroaromaticcompound such as a 6-membered N-heteroaromatic compound. Such 5- or6-membered N-heteroaromatic compounds can have a pK_(a) of at least 10and up to and including 22. An experimental method for measuring pK_(a)and the pKa values of some N-heteroaromatic bases are known (forexample, see Kalijurand et al. J. Org. Chem. 2005, 70, 1019).

In general, each 5- or 6-membered N-heteroaromatic compound isnon-polymeric in nature and has a molecular weight of 200 or less. By“5- or 6-membered,” it is meant that the N-heteroaromatic compound haseither κ or 6 atoms in the heterocyclic aromatic ring, at least one ofwhich atoms is a nitrogen atom. In general, such heterocyclic aromaticrings generally have at least one carbon atom and at least one nitrogenatom in the ring.

In Structure (I) shown above, c is 1, 2, 3, or 4, and in the embodimentswhere c is 2, 3, or 4, the multiple 5- or 6-membered N-heteroaromaticcompound molecules within the single complex molecule can be the same ordifferent. For example, the 5- or 6-membered N-heteroaromatic compoundcan be selected from the group consisting of pyridine, 2-methylpyridine,4-methylpyridine, 2,6-dimethylpyridine, 2,3-dimethylpyridine,3,4-dimethylpyridine, 4-pyridylacetone, 3-chloropyridine,3-fluoropyridine, oxazole, 4-methyloxazole, isoxazole,3-methylisoxazole, pyrimidine, pyrazine, pyridazine, and thiazole.

Representative 5- or 6-membered N-heteroaromatic compounds can bereadily obtained from various commercial chemical suppliers located invarious countries.

Further details of properties, representative compounds, and methods ofmaking them are provided in copending and commonly assigned U.S. Ser.No. 15/231,804 (filed Aug. 9, 2016 by Shukla), the disclosure of whichis incorporated herein by reference. Of these types of reducible silverion-containing complexes, a silver α-oxycarboxylate pyridine complexsuch as silver lactate pyridine complex, is particularly useful.

(vi) Still other useful silver complexes are designed with one or two(b) reducible silver ions as described above for the (iv) silvercomplexes, complexed with both one or two α-oxy carboxylate molecules asdescribed above for the (iv) silver complexes, and one, two, three, orfour primary alkylamine molecules. In general, such useful silvercomplexes can be represented by the following Structure (IV):

(Ag⁺)_(a)(L)_(b)(P)_(c)  (IV)

wherein L represents the α-oxy carboxylate; P represents the primaryalkylamine; a is 1 or 2; b is 1 or 2; and c is 1, 2, 3, or 4, providedthat when a is 1, b is 1, and when a is 2, b is 2.

In such complexes, P is a primary alkylamine having a boiling point ofless than or equal to 175° C., or having a boiling point of less than orequal to 125° C., or even at least 75° C. and up to and including 125°C., at atmospheric pressure. The useful primary alkyl amines thatgenerally have a molecular weight of less than 500 and are thusconsidered “non-polymeric” as defined by molecular weight and boilingpoint.

The term “primary alkylamine” refers herein to compounds that arenon-aromatic and are not cyclic in structure. They generally have one ormore nitrogen atoms as long as all other features (molecular weight,pKa, boiling point, and oxidation potential) described herein are met.In such compounds, each of the nitrogen atoms has two valences filled byhydrogen atoms and the remaining valence of each nitrogen atom is filledwith a substituted or unsubstituted alkyl group (not including alkylarylgroups such as benzyl groups), or with a substituted or unsubstitutedalkylene group for compounds defined herein as “primary alkyl diamines”that can be illustrated by the following Structure (V):

H₂N—R₅—NH₂  (V)

wherein R₅ represents a substituted or unsubstituted, branched orlinear, divalent alkylene group having 1 to 5 carbon atoms; and optionalsubstituents include but are not limited to, fluoride atoms for any ofthe hydrogen atoms in the alkylene group.

In most useful embodiments, the primary alkyl amines comprise a singlenitrogen atom and a single substituted or unsubstituted, branched orlinear alkyl group having at least 3 carbon atoms, and generally from 3to 6 carbon atoms, wherein any of the hydrogen atoms of the alkyl groupcan be replaced with a fluorine atom.

Representative useful primary alkylamines can be selected from the groupconsisting of a propylamine, n-butylamine, t-butylamine, isopropylamine,2,2,2-trifluoroethylamine, 2,2,3,3,3-pentafluoropropylamine,3,3,3-trifluoropropylamine, 1,2-dimethylpropylamine, t-amyl amine, andisopentylamine. Other useful primary alkylamines would be readilyapparent to one skilled in the art. In some embodiments, the primaryamine has an asymmetric carbon center on an alkyl chain. Some examplesof such amines include but not limited to, a 2-amino-3-methylbutane,3,3-dimethyl-2-butylamine, 2-aminohexane, sec-butylamine, and othersthat would be readily apparent to one skilled in the art from theforegoing description. Such primary alkylamines can be substituted withother groups that would be readily apparent to one skilled in the art.

Useful primary alkyl amines can be readily obtained from variousworldwide commercial sources of chemicals.

Further details of properties, representative compounds, and methods ofmaking them are provided in copending and commonly assigned U.S. Ser.No. 15/231,837 (filed Aug. 9, 2016 by Shukla), the disclosure of whichis incorporated herein by reference.

(vii) Yet other useful reducible silver ion-containing complexes aredesigned with one or two (b) reducible silver ions as described abovefor the (iv) silver complexes, complexed with both one or two α-oxycarboxylate molecules as described above for the (iv) silver complexes,and one, two, three, or four oxime compound molecules. In general, eachuseful silver complex can be represented by the following Structure(VI):

(Ag⁺)_(a)(L)_(b)(P)_(c)  (VI)

wherein L represents the α-oxy carboxylate; P represents an oximecompound; a is 1 or 2; b is 1 or 2; and c is 1, 2, 3, or 4, providedthat when a is 1, b is 1, and when a is 2, b is 2.

In the noted Structure (VI), the “P” compound is an oxime compound (or amixture of two or more different oxime compounds). Traditionally, an“oxime” has a general formula of >C═N—OH. In the present invention, theterm “oxime compound” is meant to include such compounds as well ascompounds in which the hydrogen is replaced with a suitable monovalentradical. In general, the oxime compounds useful herein are not polymericin nature and each has a molecular weight of 200 or less, or of 150 orless.

In Structure (VI) shown above, c is 1, 2, 3, or 4, and in theembodiments where c is 2, 3, or 4, the P molecules within the singlecomplex molecule can be the same or different oxime compounds.

For many embodiments, P can be an oxime compound that can be representedby the following Structure (VII):

wherein R₅ and R₆ are independently hydrogen or a substituted orunsubstituted alkyl group having 1 to 6 carbon atoms (linear orbranched), provided that at least one of R₅ and R₆ is one of such alkylgroups. Alternatively, R₅ and R₆ can together represent the carbon atomssufficient to provide a substituted or unsubstituted 5- or 6-membered,saturated carbocyclic ring, such as a substituted or unsubstitutedpentane ring or substituted or unsubstituted cyclohexane ring.

R₇ is hydrogen, a substituted or unsubstituted alkyl group having 1 to 6carbon atoms (linear or branched), a substituted or unsubstituted acylgroup having 1 to 6 carbon atoms (linear or branched), a —C(═O)R₈ group,or a carbonyloxyalkyl group [—C(═O)OR₈], wherein R₈ is hydrogen or asubstituted or unsubstituted alkyl having 1 to 6 carbon atoms (linear orbranched).

Representative oxime compounds useful in the practice of the presentinvention include but are not limited to, acetoxime (acetone oxime),acetaldoxime, Aldicarb, dimethylglyoxime, methylethyl ketone oxime,propionaldehyde oxime, cyclohexanone oxime, cyclopentanone oxime,heptanal oxime, acetone-O-methyl oxime, acetaldehyde-O-methyl oxime,propionaldehyde-O-methyl oxime, butanaldehyde-O-methyl oxime,2-butanone-O-methyl oxime, cyclopentanone-O-methyl oxime, and2-butanone-O-ethyl oxime.

Some representative oxime compounds can be readily obtained from variouscommercial chemical suppliers such as Sigma Aldrich. Further details ofproperties, representative examples, and methods of making them areprovided in copending and commonly assigned U.S. Ser. No. 15/362,868(filed Nov. 29, 2016 by Shukla et al.), the disclosure of which isincorporated herein by reference.

In the non-aqueous silver precursor composition, according to thepresent invention, the amounts of the (b) reducible silver ions can bevaried depending upon the particular manner in which the composition isto be used. In general, the (b) reducible silver ions are present in thepremix solution (described below) at a weight ratio to the one or more(a) polymers of at least 5:1 and up to and including 50:1, or even atleast 5:1 and up to and including 20:1, as described above.

(c) Organic Solvents Used in Making of Silver Nanoparticles

The organic solvent(s) used in the practice of this invention are notparticularly limited as long as the nitrogenous base and compoundscontaining (b) reducible silver ions can be readily dissolved ordispersed therein. It is useful that each (c) organic solvent used inthe non-aqueous silver precursor composition or the non-aqueoussilver-containing dispersion (described below) has a boiling pointgreater than or equal to 90° C., or at least 100° C., at least 150° C.and at least >200° C. but generally less than 500° C. If two or moredifferent organic solvents are used, the difference of the boilingpoints of any two organic solvents can be greater than >10° C.

In the practice of the present invention, the (c) organic solventsuseful in the practice of this invention can be selected to have a totalHansen parameter that is compatible with the total Hansen parameter(δ_(T) ^(Polymer)) of the one or more (a) polymers (such as one or morecellulosic polymers) that are to be incorporated into the silvernanoparticle composite. It is desirable that the total Hansen parametersof the one or more (a) polymers and the one or more (c) organic solventslie within a certain range, and it is especially desirable to maintainthe desired total Hansen parameter as the organic solvent profilechanges during the deposition processes. Typically, the (c) organicsolvents have a total Hansen parameter (δ_(T) ^(Solvent)) equal to orgreater than the total Hansen parameter (δ_(T) ^(Polymer)) of the one ormore (a) polymers (such as one or more cellulosic polymers). Thus, if amixture of (c) organic solvents is used, it is desirable that the totalHansen parameter of the organic solvent mixture is equal to or greaterthan the total Hansen parameter of the one or more (a) polymers (such asone or more cellulosic polymers) to be incorporated within the silvernanoparticle composite. Some useful dispersions comprise organic solventblends that maintain desirable total Hansen parameters even as the (c)organic solvents are removed during and after the deposition processes(described below).

Thus, in all embodiments of the non-aqueous silver precursorcomposition, the (a), (b), (d), and (e) components are dispersed ordissolved in an (c) organic solvent medium that consists of one or moreorganic solvents described herein, and especially one or more hydroxylicorganic solvents, each of which has an α-hydrogen atom and propertiesdefined below. It is particularly useful that the (a) polymer(s) aresoluble in the one or more (c) organic solvents.

Useful hydroxylic solvents can be alcohols having an α-hydrogen atom.Accordingly, primary and secondary alcohols are useful and they can bemonohydric or polyhydric. While either saturated or unsaturated alcoholscan be used, it is desirable that the alcohol used be free from olefinicunsaturation. Suitable alcohols can be of either straight-chain orbranched-chain configuration, and can contain in their structure eitheror both of alicyclic or aromatic carbon-to-carbon moieties.Representative examples of suitable straight-chain primary alcoholsinclude but are not limited to, ethanol, n-propanol, n-butanol,n-pentanol, n-hexanol, 1-octanol, 2-ethyl-1-hexanol, n-decanol, ethyleneglycol, propylene glycol, and benzyl alcohol. Representative examples ofbranched-chain alcohols include isobutyl alcohol, isoamyl alcohol, andsecondary butyl carbinol. Secondary alcohols have greater reactivity.Representative examples of secondary alcohols include but are notlimited to, isopropyl alcohol, secondary butyl alcohol, secondary amylalcohol, diethyl carbinol, methyl isobutyl carbinol, methyl-3-heptanol,diisobutyl carbinol, dodecanol-Z, methyl allyl carbinol, cyclohexanol,methyl cyclohexyl carbinol, phenyl methyl carbinol, and similarmaterials. Combinations of any of these alcohols can be used if desired.Such materials can be readily purchased from various commercial sourcesor readily prepared using known starting materials, conditions, andreaction schemes.

Glycol ethers with both an ether and alcohol functional group in thesame molecule are particularly useful in the practice of the presentinvention. Representative examples of such glycol ethers include but arenot limited to, 2-methoxyethanol, 2-ethoxyethanol, diethylene glycolmonoethyl ether (carbitol), and methoxy isopropanol. Mixtures of thesecompounds can be used if desired. Such glycol ethers are commerciallyavailable.

Minor amounts of water can be present, but the total weight % of waterin the non-aqueous silver precursor composition is generally less than10%.

(d) Nitrogenous Bases:

Another essential component of the non-aqueous silver precursorcompositions according to the present invention is a nitrogenous basehaving a pKa in acetonitrile of at least 15 and up to and including 25at 25° C. Such one or more nitrogenous bases are generally present in anequimolar amount or molar excess relative to the amount of (b) reduciblesilver ions, described above.

In general, the nitrogenous bases can be cyclic or acyclic alkyl amines.All primary amines, secondary amines, or tertiary amines are useful inthe present invention. Some especially useful amines are1,4-diazabicyclo[2.2.2]octane (DABCO), cyclohexylamine, pipperidine,N-methyl pipperidine, N-methyl-3-piperidinol, and others that would bereadily apparent to one skilled in the art. Combinations of two or moreof these compounds can be used if desired.

The nitrogenous base can be an alkanolamines including but are notlimited to, ethanol amine, 2-(ethylamino)ethanol,2-(methylamino)ethanol, 2-(butylamino)ethanol, methyldiethanolamine(MDEA), diethanolamine (DEA), diglycolamine (DGA), diethylaminoethanol(DEAE), and others that would be readily apparent to one skilled in theart. Combinations of two or more of these compounds can be used ifdesired.

Nitrogen-containing heterocyclic compounds are also useful asnitrogenous bases in the present invention. Such compounds can be arearomatic and heterocyclic in nature and comprise at least one nitrogenatom in the aromatic heterocyclic ring. Such compounds can also besubstituted or unsubstituted as desired. Representative aromaticheterocyclic, nitrogen-containing bases useful in this invention includebut are not limited to, substituted or unsubstituted, non-polymericpyridine, picolines, lutidines, quinoline, purine, isoquinoline,imidazole, benzimidazole, benzthiazole, thiazole, oxazole, benzoxazole,4,4′-bipyridine, pyrazine, triazine, pyrimidine, nicotinic acid, andisonicotinic acid compounds. Mixtures of two or more these or otherunnamed compounds can be used if desired, in any useful proportion. Thesubstituted or unsubstituted pyridines are particularly useful.

Other useful nitrogenous bases include amidines such as1,8-diazabicyclo[5.4.0]undec-7-ene (DBU).

It is essential that the nitrogenous base has a pKa of at least 15 andup to and including 20, or more typically of at least 18 and up to andincluding 25, as measured in acetonitrile. An experimental method formeasuring pKa, and the pKa values of some aromatic heterocyclic andamine nitrogenous bases are known (for example, see Kalijurand et al. J.Org. Chem. 2005, 70, 1019; and Cantu et al. Journal of Chromatography A,2005, 1068, 99).

In general, each nitrogenous base used in the present invention is inliquid form and has a boiling point equal to or higher than each of the(c) one or more organic solvents, for example, each of the one or morehydroxylic solvents. Thus, the boiling point of the nitrogenous base atatmospheric pressure is at least 100° C. and up to but less than 500°C., or at least 120° C. and up to and including 350° C., or up to andincluding 250° C.

The one or more (d) nitrogenous bases can provided in a molar amount ofat least 1:1 to and including 3:1 relative either the (b) reduciblesilver ions or (b′) reducible copper ions in the practice of the methodof this invention.

Useful nitrogenous bases can be readily obtained from commercialsources.

(e) Ascorbic Acid

Ascorbic acid, also known as Vitamin C or L-ascorbic acid, can beobtained from various commercial sources for use in the presentinvention. It is generally used in the present invention in relation tothe reducible silver ions or reducible copper ions at an at least 0.01:1molar ratio, or at a molar ratio of at least 0.02:1 to 2:1, but theascorbic acid can be present in excess if desired, in relation to such(b) reducible silver ions or (b′) reducible copper ions. In addition,the ascorbic acid can be present in the non-aqueous silver precursorcomposition in an amount of at least 1:3 and to and including 2:1, oreven at least 1:2 and to and including 1.5:1, molar ratio with respectto the total amount of the one or more (d) nitrogenous bases present inthe non-aqueous silver precursor composition. A skilled worker wouldknow how to balance the desirable amounts of ascorbic acid, nitrogenousbase, and reducible silver or copper ions, to achieve desirable results.

Where compounds possess more than one or more asymmetric center, theymay exist as “stereoisomers”, such as enantiomers and diastereomers.Ascorbic acid has two chiral centers and so there are fourstereoisomers. It is to be understood that all such stereoisomers andmixtures thereof in any proportion are encompassed within the scope ofthe present invention.

Non-Aqueous Copper Precursor Compositions

For all embodiments, the non-aqueous copper precursor compositionsaccording to the present invention contain five essential components forpurposes of providing copper metal in the form of copper nanoparticlesaccording to the present invention: one or more (a) polymers (such asone or more cellulosic polymers) as described above; (b′) reduciblecopper ions in the form of one or more copper salts or copper complexesas described below; an organic solvent medium consisting of (c) or moreorganic solvents, as described above; (d) one or more nitrogenous bases,as described above; and (e) ascorbic acid as described above. No othercomponents are purposely added to the non-aqueous copper precursorcompositions according to the present invention in order to achieve theinventive advantages or purposes, and as noted above, water is notpurposely included. As described below, for some embodiments, (f) carbonblack can be present as a sixth essential component.

Upon thermal treatment, as described below, the non-aqueous copperprecursor composition according to this invention can be converted intoa corresponding non-aqueous dispersion or non-aqueous copper-containingdispersion comprising a copper nanoparticle composite comprising bothcopper and one or more (a) polymers as described above. It is desirablethat at least 90 mol %, at least 95 mol %, or even at least 98 mol %(which means “substantially all”) of the (b′) reducible copper ions areconverted to copper during this process.

The one or more (a) polymers, (b′) reducible copper ions, (c) organicsolvents, (d) nitrogenous bases, and (e) ascorbic acid can be combinedin general by mixing them under suitable ambient conditions so thatthermal reduction does not occur prematurely to any appreciable extent.In general, the (a), (c), (d), and (e) components can be formulated ormixed to form a premix solution and at room temperature or underappropriate heating, the (b′) reducible copper ions can be added to thepremix solution in a controlled fashion. Details of this method aredescribed below.

Ultimately, the non-aqueous copper precursor composition is formed, andit generally has at least 1% solids and up to and including 70% solids,or more typically of at least 5% solids and up to and including 25%solids. The amount of solids, and (c) organic solvents, and viscosity,can thus be adjusted for a particular use or copper ion reductionoperation.

The non-aqueous copper precursor composition is generally in liquid formhaving a viscosity of at least 1 centipoise (0.001 Pascal sec) and up toand including 5,000 centipoise (5 Pascal sec), or more likely aviscosity of at least 3 centipoise (0.003 Pascal sec) and up to andincluding 50 centipoise (0.05 Pascal sec), all measured at 25° C.

The non-aqueous (copper-containing) dispersion described below can havethe same or different viscosity as the corresponding non-aqueous copperprecursor composition. In most embodiments, the two compositions haveessentially the same viscosity, that is, no more than 10% difference.

(b′) Reducible Copper Ions

Reducible copper ions can be provided in the non-aqueous copperprecursor composition from many sources as long as each copper salt orcopper complex in which they are provided is soluble within the one ormore (c) hydroxylic organic solvents at an amount of at least 1 g/literat 20° C.

In general, copper salts or copper complexes comprised of reduciblecopper ions and any suitable organic or inorganic anion or complexedmoiety (or a combination of anions and complexed moieties) can be usedin the practice of the present invention to provide the (b′) reduciblecopper ions for the present invention. Such copper complexes can bemononuclear, dinuclear, trinuclear, or higher and each compoundgenerally has a net neutral charge. Such reducible copper ion-containingmaterials can be readily purchased from various commercial sources orprepared using known procedures, starting materials, and reactionconditions unless otherwise indicated.

A first class of reducible copper ion-containing compounds are coppersalts having organic or inorganic anions. Some representative coppersalts include but not limited to, cupric nitrate, copper sulfate, copperchloride, copper nitrate, copper acetylacetonate, copper acetate,cuprous oxide, cupric oxide, and other copper salts that would bereadily apparent to one skilled in the art.

Non-Aqueous Silver-Containing Dispersions

The reducible silver ions in a non-aqueous silver precursor compositionaccording to the present invention can be converted into silvernanoparticles in silver nanoparticle composites to provide acorresponding non-aqueous silver-containing dispersion using theoperations described below for the methods according to this invention.

Such non-aqueous silver-containing dispersions comprise one or moresilver nanoparticle composites, each comprising silver metal and one ormore of the (a) polymers described above. The amount of such silvernanoparticle composites in the non-aqueous silver-containing dispersionwould generally be the total weight of silver and (a) polymers in thenon-aqueous silver-containing dispersion but it could be less, dependingupon how much of the (h) reducible silver ions are reduced and how muchfree silver, (b) reducible silver ions, and free (a) polymers arepresent in the non-aqueous silver-containing dispersion after silver ionreduction, silver nanoparticle composite isolation, and re-dispersion(described below).

As noted above, it is desired that a high amount of the reducible silverions be converted to silver metal and thus, the non-aqueoussilver-containing dispersion would contain silver in an amount of up toand including 100 mol % of the original (b) reducible silver ions in thenon-aqueous silver precursor composition.

The non-aqueous silver-containing dispersion contains one or more (c)organic solvents (such as hydroxylic organic solvents) as describedabove. Such organic solvents can be same or different as those used tomake the non-aqueous silver precursor compositions. These (c) organicsolvents can be those originally in the non-aqueous silver precursorcomposition (that is, before isolation and re-dispersion of the silvernanoparticle composite), or they can be added during re-dispersion ofthe silver nanoparticle composite.

(d) Nitrogenous base is also generally present in the non-aqueoussilver-containing dispersion although much of the original amount thatwas present in the non-aqueous silver precursor composition may bewashed out during isolation of the silver nanoparticle composite.However, it is evident that some (d) nitrogenous base remains with thesilver nanoparticle composite upon its re-dispersion in one or more (c)organic solvents. The amount of such nitrogenous base(s) in thenon-aqueous silver-containing dispersion is generally up to andincluding 10 weight %, based on the total weight of silver metal (notincluding any remaining reducible silver ions).

Silver can be present in the non-aqueous silver-containing dispersion ata weight ratio to the (a) one or more polymers of at least 5:1 and up toand including 20:1.

Moreover, the non-aqueous silver-containing dispersion can have aviscosity of at least 1 centipoise (0.001 Pascal sec) and up to andincluding 5000 centipoise (5 Pascal see) at 25° C.

Non-Aqueous Copper-Containing Dispersions

The reducible copper ions in a non-aqueous copper precursor compositionaccording to the present invention can be converted into coppernanoparticles in silver nanoparticle composites to provide acorresponding non-aqueous copper-containing dispersion using theoperations described below for the methods according to this invention.

Such non-aqueous copper-containing dispersions comprise one or morecopper nanoparticle composites, each comprising copper metal and one ormore of the (a) polymers described above. The amount of such coppernanoparticle composites in the non-aqueous copper-containing dispersionwould generally be the total weight of copper and (a) polymers in thenon-aqueous copper-containing dispersion but it could be less, dependingupon how much of the (b′) reducible copper ions are reduced and how muchfree copper, (b′) reducible copper ions, and free (a) polymers arepresent in the non-aqueous copper-containing dispersion after copper ionreduction, copper nanoparticle composite isolation, and re-dispersion(described below).

As noted above, it is desired that a high amount of the reducible copperions be converted to copper metal and thus, the non-aqueouscopper-containing dispersion would contain copper in an amount of up toand including 100 mol % of the original (b) reducible copper ions in thenon-aqueous copper precursor composition.

The non-aqueous copper-containing dispersion contains one or more (c)organic solvents (such as hydroxylic organic solvents) as describedabove. Such organic solvents can be same or different as those used tomake the non-aqueous copper precursor compositions. These (c) organicsolvents can be those originally in the non-aqueous copper precursorcomposition (that is, before isolation and re-dispersion of the coppernanoparticle composite), or they can be added during re-dispersion ofthe copper nanoparticle composite.

(d) Nitrogenous base may also be present in the non-aqueouscopper-containing dispersion although much of the original amount thatwas present in the non-aqueous copper precursor composition may bewashed out during isolation of the silver nanoparticle composite.However, it is evident that some (d) nitrogenous base remains with thecopper nanoparticle composite upon its re-dispersion in one or more (c)organic solvents. The amount of such nitrogenous base(s) in thenon-aqueous copper-containing dispersion is generally up to andincluding 10 weight %, based on the total weight of silver metal (notincluding any remaining reducible copper ions).

Copper can be present in the non-aqueous silver-containing dispersion ata weight ratio to the (a) one or more polymers of at least 5:1 and up toand including 20:1.

Moreover, the non-aqueous copper-containing dispersion can have aviscosity of at least 1 centipoise (0.001 Pascal sec) and up to andincluding 5000 centipoise (5 Pascal sec) at 25° C.

(f) Carbon Black:

In some embodiments, (f) carbon black can be incorporated into thenon-aqueous silver-containing dispersions or non-aqueouscopper-containing dispersions at a suitable time. Carbon black can beobtained commercially in various forms. The (f) carbon black can beadded so that it is present in an amount of at least 5 weight %, basedon (or relative to) the total weight of the one or more (a) polymers.Typically, the amount of (f) carbon black is at least 5 weight % and upto and including 50 weight %, or more typically in an amount of at least5 weight % and up to and including 25 weight %, based on (or relativeto) the total weight of the one or more (a) polymers.

Articles

The non-aqueous silver-containing dispersions prepared according to thepresent invention can be used to provide articles that can then be usedin various operations or devices.

An article (or element) is typically designed to have a substrate havingthereon a dry layer or dry pattern comprising either a silvernanoparticle composite composition or a copper nanoparticle compositecomposition. Thus, the article has silver nanoparticles or coppernanoparticles and no appreciable amounts of (b) reducible silver ions or(b′) reducible copper ions, respectively. That is, the (b) reduciblesilver ions or (b′) reducible copper ions are generally present in anamount of less than 5 mol %, based on the total amount of silver, orcopper, respectively, in the dry layer or dry pattern.

Thus, each article comprises a substrate (described below), and can havedisposed on at least one supporting surface (or side) thereof a drylayer or dry pattern of either a dry silver nanoparticle compositecomposition or a dry copper nanoparticle composite composition, eachcomprising:

either a silver nanoparticle composite comprised of silver nanoparticlesand both (a) one or more polymers and (e) ascorbic acid adsorbed on thesilver nanoparticles; or a copper nanoparticle composite comprised ofcopper and both (a) one or more polymers and (e) ascorbic acid adsorbedon the copper nanoparticles, each of the (a) one or more polymersselected from one or more of cellulose acetate, cellulose acetatephthalate, cellulose acetate butyrate, cellulose acetate propionate,cellulose acetate trimellitate, hydroxypropylmethyl cellulose phthalate,methyl cellulose, ethyl cellulose, hydroxyethyl cellulose,hydroxypropylmethyl cellulose, carboxymethyl cellulose, and combinationsthereof; and one or more nitrogenous bases as described above.

These silver nanoparticle composites or copper nanoparticle composites,each generally have a mean particle size (d50) of at least 10 nm and upto and including 1500 nm, or of at least 20 nm and up to and including500 nm, or even of at least 50 nm and up to and including 350 nm.

Carbon black can also be present in either the dry silver nanoparticlecomposite composition or copper nanoparticle composite composition in anamount of up to and including 50 weight %, or at least 5 weight % and upto and including 50 weight %, or even at least 5 weight % and up to andincluding 25 weight %, all based on (or relative to) the total weight ofthe one or more (a) polymers.

Such dry layers or dry patterns generally contain less than 5 mol %, orless than 2 mol %, or even less than 1 mol %, of (b) reducible silverions, or (b′) reducible copper ions, all based on the total molar amountof silver, or copper, respectively in the dry pattern or dry layer.

When one or more dry patterns of either a silver nanoparticle compositecomposition or copper nanoparticle composite composition are formed onthe substrate, at least one of the patterns can comprise a combinationof fine lines, each fine line having an average dry width of at least 1μm and up to and including 20 μm, which combination of fine lines can bearranged in parallel, crossing at any desired angle, a combinationthereof, or in a random arrangement. Each dry pattern can be designed tohave any predetermined grid pattern that can be achieved in the art.

The presence of the (f) carbon black in the dry patterns is particularlyadvantageous when the substrate (described in detail below) istransparent, such as a transparent continuous polymeric film (forexample a transparent continuous polycarbonate, polystyrene, orpolyester film).

In many embodiments of articles, the substrate has a first supportingsurface (or side) and a second opposing supporting surface (or side),and one or more dry patterns of either the silver nanoparticle compositecomposition of copper nanoparticle composite composition are disposed onthe first supporting surface, and optionally, one or more dry patternsof the same or different silver nanoparticle composite composition orcopper nanoparticle composite composition are disposed on the secondopposing supporting surface. The dry patterns can be disposed on the twoopposing supporting surfaces of the substrate in any opposingarrangement, that is either directly opposite one another, or offset insome desired arrangement.

For example, in some embodiments of the article, the substrate is atransparent continuous polymeric (such as polyester) film (or web) thathas a first supporting surface and a second opposing supporting surface,

the article further comprising multiple (two or more) individual drypatterns formed on the first supporting surface comprise the same ordifferent silver nanoparticle composite composition or coppernanoparticle composite composition, and further comprising multiple (twoor more) individual dry patterns formed on the second opposingsupporting surface which opposing multiple dry patterns comprise thesame or different silver nanoparticle composite composition or coppernanoparticle composite composition.

For example, in such embodiments, all of the multiple individual drypatterns on both the first supporting surface and the second opposingsupporting surface can comprise the same silver nanoparticle compositecomposition or copper nanoparticle composite composition, the silvernanoparticle composite composition or copper nanoparticle compositecomposition in each individual dry pattern comprises silver nanoparticlecomposite(s) or copper nanoparticle composite(s) having a mean particlesize (d50) of at least 50 nm and up to and including 300 nm, and each ofthe multiple individual dry patterns comprises fine lines having anaverage dry width of at least 1 μm and up to and including 20 μm.

The articles described herein comprise a suitable substrate thatgenerally has two planar surfaces: a first supporting side (or surface)and a second opposing supporting side (or surface). Such substrates canhave any suitable form such as sheets of any desirable size and shape,webs of metals, films, and elongated fibers or woven fibers (such as inwebs of textiles) or other porous materials, and especially continuouswebs of various transparent, translucent, or opaque polymeric materials(such as polycarbonates and polyesters) that can be supplied, used, orstored as rolls. Such continuous polymeric webs or films can be used incontinuous roll-to-roll manufacturing operations where the continuousweb is unrolled from a supply roll and taken up using a take-up roll.

More specifically, a uniform thin film or one or more thin film patternsof either a silver nanoparticle composite composition or coppernanoparticle composite composition are provided in a suitable manner onone or more supporting sides of a suitable substrate to provide anarticle as described according to the methods described below.Typically, such articles have an initially “wet” non-aqueoussilver-containing (or copper-containing) dispersion layer or patternduring and immediately after application to the substrate but thehydroxylic organic solvents can be removed as described below to providethe desired uniform thin film layer or one or more thin film patterns.

Suitable substrates can be composed of any suitable material that doesnot inhibit the purpose of the present invention and eventual uses ofthe articles. For example, substrates can be formed from materialsincluding but are not limited to, polymeric films, metals, glasses(untreated or treated for example with tetrafluorocarbon plasma,hydrophobic fluorine, or a siloxane water-repellant material), siliconor ceramic materials such as ceramic wafers, fabrics, papers, andcombinations thereof (such as laminates of various films, or laminatesof papers and films) provided that a uniform thin film or thin filmpattern can be formed thereon in a suitable manner and followed bythermal treatment (heating) on at least one supporting surface thereof.The substrate can be transparent, translucent, or opaque, and rigid orflexible. The substrate can include one or more auxiliary polymeric ornon-polymeric layers or one or more patterns of other materials beforethe non-aqueous dispersion is applied according to the presentinvention.

More specifically, suitable substrate materials for forming precursorand product articles according to the present invention include but arenot limited to, metallic films or foils, metallic films on polymer,glass, or ceramic materials, metallic films on electrically conductivefilm supports, semi-conducting organic or inorganic films, organic orinorganic dielectric films, or laminates of two or more layers of suchmaterials. Useful substrates can include transparent polymeric filmssuch as poly(ethylene terephthalate) films, poly(ethylene naphthalate)films, polyimide films, polycarbonate films, polyacrylate films,polystyrene films, polyolefin films, and polyamide films, silicon andother ceramic materials, metal foils such as aluminum foils, cellulosicpapers or resin-coated or glass-coated papers, glass or glass-containingcomposites, metals such as aluminum, tin, and copper, and metalizedfilms. Porous fabrics, glasses, and polymeric webs can also be used.

Particularly useful substrates including continuous flexible polymericfilms, metal foils, and textile webs. Useful continuous flexiblepolymers films include transparent continuous polymeric films such astransparent continuous polyester films such as films of poly(ethyleneterephthalate), polycarbonate films, or poly(vinylidene chloride) filmswith or without surface-treatments or coatings as noted below.

For example, either or both supporting surfaces of the substrate can betreated with a primer layer or receptive layer, or with electrical ormechanical treatments (such as graining) to improve adhesion of eitherthe silver nanoparticle composite composition or copper nanoparticlecomposite composition. An adhesive layer can be thermally activated,solvent activated, or chemically activated. A separate receptive layercan have any suitable dry thickness of at least 0.05 μm when measured at25° C.

The two supporting surfaces of the substrate, especially polymericsubstrates, can be treated by exposure to corona discharge, mechanicalabrasion, flame treatments, or oxygen plasmas, or coated with variouspolymeric films, such as poly(vinylidene chloride) or an aromaticpolysiloxane.

Useful substrates can have a desired dry thickness depending upon theeventual use of the articles. For example, the substrate dry thickness(including all treatments and auxiliary layers) can be at least 0.001 mmand up to and including 10 mm, and especially for transparent polymericfilms, the substrate dry thickness can be at least 0.008 mm and up toand including 0.2 mm.

The substrate used in the articles described herein can be provided invarious forms, such as for example, individual sheets of any size orshape, and continuous webs such as continuous webs of transparentsubstrates (including transparent continuous polyester films). Suchcontinuous webs can be divided or formed into individual first, second,and additional portions on a first supporting surface and a secondopposing supporting surface on which can formed the same or differentcorresponding silver nanoparticle composite composition (or coppernanoparticle composite composition) patterns in the different (orindividual) portions of a supporting side (such as the first supportingsides).

Method for Forming Silver-Containing or Copper-Containing Dispersions

While the following discussion relates to forming silver-containingdispersions according to the present invention, it is to be understoodthat copper-containing dispersions can be formed in a similar mannerusing the corresponding reducible copper ions from one or more suitablecopper salts or complexes described above.

Non-aqueous silver-containing dispersions according to the presentinvention comprising the silver nanoparticle composite described abovecan be provided using the method according to the present invention. Inthis method, the one or more (a) polymers (as described above) are mixed(or dissolved) in one or more (c) organic solvents (described above)using suitable stirring and mixing conditions, along with a suitable (d)nitrogenous base and (e) ascorbic acid.

Thus, one or more (d) nitrogenous base(s) (as described above) and (e)ascorbic acid are mixed within the one or more (c) organic solvents (asdescribed above) along with the one or more (a) polymers (as describedabove), all in suitable amounts described above, to form a premixsolution. Reactions between components in this premix solution begin tooccur immediately even at room temperature (for example, 20-25° C.) butthe premix solution can also be heated to a temperature of at least 40°C. and more likely to a temperature of at least 75° C. and up to andincluding 125° C. using any suitable heating means. While at roomtemperature or during the heating operation, the premix solution can becontinuously stirred using suitable stirring mechanism or apparatus.

While keeping this premix solution stirred at the noted temperature, forexample of at least 40° C., a solution of (b) reducible silver ions (inany silver ion-containing form as described above) in one or more (c)organic solvents (same or different from those already in premixsolution) can be added to the premix solution. The rate of addition of(b) reducible silver ions can be varied, for example, by using aperistaltic pump. This addition process is generally at a ratesufficient at the noted temperature to promote the extensive reductionof the (b) reducible silver ions, for example at least 90 mol %reduction based on the original amount of (b) reducible silver ions. Ingeneral, the final amount of added (b) reducible silver ions in thepremix solution is equimolar or less in relation to the (d) nitrogenousbase(s) present in the premix solution. In addition, the final weightratio of the (b) reducible silver ions to the one or more (a) polymersis at least 5:1 and up to and including 50:1, or at least 60:1 and up toand including 75:1.

The result of this addition operation is the relatively rapid formationof one or more silver nanoparticle composites in a reaction mixture.

If (f) carbon black is to be included in the non-aqueoussilver-containing dispersion, it can be incorporated and dispersedwithin at any suitable point during the method in appropriate amountsdescribed above using a suitable mixing means such as a shear mixer.Suitable shear mixers are commercially available from various sourcessuch as Silverson, Admix, and Ross.

The resulting silver nanoparticle composite in the reaction mixture canbe cooled generally to room temperature (20-25° C.). The cooled silvernanoparticle composite generally can then be isolated from the reactionmixture by either of the following two methods:

1) gravity precipitation followed by filtration of the precipitate; or

2) pouring the cooled reaction mixture into water and then filtering offthe precipitate.

The isolated silver nanoparticle composite can be dried, if desired, andstored for later use. Alternatively, the silver nanoparticle compositecan be immediately re-dispersed in one or more suitable (c) organicsolvents (same as or different from those used above) to provide anon-aqueous silver-containing dispersion containing up to 80 weight % ofsilver nanoparticle composite.

Particularly useful (c) organic solvents used for this dispersingoperation have a total Hansen parameter that is compatible with thetotal Hansen parameter of the one or more (a) polymers (such as one ormore cellulosic polymers) that have been incorporated into the silvernanoparticle composite. Typically, these (c) organic solvents have atotal Hansen parameter equal to or greater than the total Hansenparameter of the one or more (a) polymers (such as one or morecellulosic polymers). Thus, if a mixture of (c) organic solvents is usedfor dispersion, it is desirable that the total Hansen parameter of theorganic solvent mixture is equal to or greater than the total Hansenparameter of the one or more (a) polymers (such as one or morecellulosic polymers) that have been incorporated within the silvernanoparticle composite.

The non-aqueous silver-containing dispersion or non-aqueouscopper-containing dispersion resulting from the method described hereincan be stored for later use or immediately employed in variousadditional operations, for example, to provide an article as describedabove.

For example, a non-aqueous silver-containing dispersion or a non-aqueouscopper-containing dispersion can be disposed onto a substrate (asdescribed above) using any suitable equipment and method as describedbelow, and the one or more (c) organic solvents can be removed in asuitable manner. Thus, the non-aqueous silver-containing dispersion ornon-aqueous copper-containing dispersion disposed onto one or moresupporting sides of a substrate to provide, upon drying, either a dryuniform film (usually thin), or one or more dry patterns of eithersilver nanoparticle composite composition or copper nanoparticlecomposite composition, respectively. Disposition of the non-aqueoussilver-containing dispersion or non-aqueous copper-containing dispersioncan be achieved in a variety of means known in the art for applyingsolutions or dispersions to a solid substrate.

For example, in some embodiments, a variety of films, includingpolymeric films composed of polyethylene, polypropylene,biaxially-oriented polypropylene, polyethylene terephthalate,polybutylene terephthalate and polyamide, can be utilized as suitabletransparent substrates. The choice of substrate structure is not,however, limited to films but includes any material that can be formedinto bags, shrink wrap, plates, cartons, boxes, bottles, crates, andother containers. The disposition on or application to a substrate canbe carried out for example, using uniform inkjet printing, gravureprinting, screen printing, flexographic printing, or by using a bladecoating, gap coating, slot die coating, X-slide hopper coating, or knifeon roll operations.

For example, a non-aqueous silver-containing dispersion or non-aqueouscopper-containing dispersion can be disposed on the substrate (one orboth supporting surfaces) in a patternwise manner using techniquesdescribed below such as flexographic printing, screen printing, gravureprinting, or inkjet printing to provide one or multiple (two or more)silver (or copper) nanoparticle composite composition patterns on thesubstrate.

For example, where the substrate has a first supporting side and asecond opposing supporting side, the method according to this inventioncan also comprise disposing either the non-aqueous silver-containingdispersion or non-aqueous copper-containing dispersion containing thesilver nanoparticle composite or copper nanoparticle composite,respectively, onto the substrate in a patternwise manner to form atleast one pattern (or multiple patterns) of the non-aqueoussilver-containing dispersion or non-aqueous copper-containing dispersionon at least the first supporting side.

It is also possible for the method according to the present invention tobe used to further dispose the same or different non-aqueoussilver-containing dispersion or non-aqueous copper-containing dispersiononto the substrate in a patternwise manner to form multiple patterns ofthe non-aqueous silver-containing dispersion or non-aqueouscopper-containing dispersion on the second opposing supporting side, orin a manner to form multiple patterns of a non-aqueous silver-containingdispersion or non-aqueous copper-containing dispersion on both the firstsupporting side and the second opposing supporting side using one ormore flexographic printing members.

The present invention lends itself to rapid conversion of (b) reduciblesilver ions to electrically-conductive silver metal in an economical wayso the process can be incorporated into the manufacture of variousdevices containing electrically-conductive silver or copper patterns.Such operations can often be achieved using a substrate that is acontinuous web that is unrolled from a supply roll and is taken up usinga take-up roll, and the method is carried out in a continuousroll-to-roll manner.

More details about useful electrically-conductive silver orelectrically-conductive copper patterns that are achievable with thepresent invention are now provided.

Any applied pattern of silver or copper nanoparticle compositecomposition can comprise a grid of electrically-conductive fine lines(or other shapes including circles or an irregular network) as describedabove and the optimal dry thickness (or width) can be tailored for anintended use.

In some embodiments, the same or different silver (or copper)nanoparticle composite pattern (after drying) can be provided in asuitable manner in different portions on both the first supporting sideand the second opposing supporting side of the substrate to form a“duplex” or dual-sided article, and such patterns can be provided usingthe same or different non-aqueous silver-containing dispersion ornon-aqueous copper-containing dispersion.

In many embodiments, either a non-aqueous silver-containing dispersionor non-aqueous copper-containing dispersion can be applied on one orboth supporting surfaces of the substrate (for example as a roll-to-rollweb) using flexographic printing with one or more elastomeric reliefelements such as those derived from flexographic printing plateprecursors, many of which are known in the art. Some such precursors arecommercially available, for example as the CYREL® FlexographicPhotopolymer Plates from DuPont and the Flexcel SR and NX Flexographicplates from Eastman Kodak Company.

Useful elastomeric relief elements are derived from flexographicprinting plate precursors and flexographic printing sleeve precursors,each of which can be appropriately imaged (and processed if needed) toprovide the elastomeric relief elements for “printing” suitableelectrically-conductive silver nanoparticle or copper nanoparticlecomposite patterns. Useful precursors of this type are described forexample, in U.S. Pat. No. 7,799,504 (Zwadlo et al.) and U.S. Pat. No.8,142,987 (Ali et al.) and U.S. Patent Application Publication2012/0237871 (Zwadlo), the disclosures of all of which are incorporatedherein by reference. Such flexographic printing precursors can compriseelastomeric photopolymerizable layers that can be imaged through asuitable mask image to provide an elastomeric relief element(flexographic printing plate or flexographic printing sleeve). Theresulting relief layer can be same or different depending upon whetherthe same or different patterns are to be formed on one or bothsupporting sides of the substrate.

In other embodiments, an elastomeric relief element can be provided froma direct (or ablation) laser-engravable elastomeric relief elementprecursor, with or without integral masks, as described for example inU.S. Pat. No. 5,719,009 (Fan), 5,798,202 (Cushner et al.), 5,804,353(Cushner et al.), 6,090,529 (Gelbart), 6,159,659 (Gelbart), 6,511,784(Hiller et al.), 7,811,744 (Figov), 7,947,426 (Figov et at), 8,114,572(Landry-Coltrain et al.), 8,153,347 (Veres et al.), 8,187,793 (Regan etal.), and U.S. Patent Application Publications 2002/0136969 (Hiller etal.), 2003/0129530 (Leinenback et al.), 2003/0136285 (Telser et al.),2003/0180636 (Kanga et al.), and 2012/0240802 (Landry-Coltrain et al.),the disclosures of all of which are incorporated herein by reference.

When the noted elastomeric relief elements are used to provide patterns,either the non-aqueous silver-containing dispersion or non-aqueouscopper-containing dispersion can be applied in a suitable manner to theuppermost relief surface (raised surface) in the elastomeric reliefelement. Then, application to a substrate can be accomplished in asuitable procedure while as little as possible is coated from the sides(slopes) or recesses of the relief depressions. Anilox roller systems orother roller application systems, especially low volume Anilox rollers,below 2.5 billion cubic micrometers per square inch (6.35 billion cubicmicrometers per square centimeter) and associated skive knives can beused. In such embodiments, the non-aqueous silver-containing dispersionor non-aqueous copper-containing dispersion can be designed to haveoptimal viscosity for flexographic printing. When a substrate is movedthrough the roll-to-roll handling system from a flexographic printingplate cylinder to an impression cylinder, the impression cylinderapplies pressure to the flexographic printing plate cylinder thattransfers an image from an elastomeric relief element to the substrate.

A substrate can be “printed” one or more times using inkjet printing,gravure printing, screen printing, or flexographic printing along a web(for example, a roll-to-roll continuous web) that can contain multiplepatterns (or individual precursor articles after cutting) in multipleportions of the continuous web that is passed through various stations.The same or different non-aqueous silver-containing dispersions ornon-aqueous copper-containing dispersions can be applied (for example,printed) on one or both supporting sides of the substrate in thecontinuous roll-to-roll production operation.

After deposition of the appropriate non-aqueous silver-containing orcopper-containing dispersion onto a substrate, for example, in apatternwise manner using flexographic printing, at least 75 weight % andup to and including 100 weight % of the (c) organic solvent(s)(described above) can be removed in any suitable manner to form anarticle. For example, ambient drying can be carried out in an openenvironment, or the article can be subject to “active” drying operationsand apparatus (for example, heated drying chamber). Useful dryingconditions can be as low as room temperature for as little as 5 secondsand up to and including several hours depending upon the manufacturingprocess. In many processes, such as roll-to-roll manufacturingoperations, drying conditions can be employed at any suitabletemperature, for example greater than 50° C. to remove at least 75weight % and up to 100 weight % of all remaining organic solvents withinat least 1 second and up to and including 10 seconds or even within 5seconds.

The present invention provides at least the following embodiments andcombinations thereof, but other combinations of features are consideredto be within the present invention as a skilled artisan would appreciatefrom the teaching of this disclosure:

1. A method comprising, in sequence:

A) mixing:

(a) one or more polymers selected from one or more of cellulose acetate,cellulose acetate phthalate, cellulose acetate butyrate, celluloseacetate propionate, cellulose acetate trimellitate, hydroxypropylmethylcellulose phthalate, methyl cellulose, ethyl cellulose, hydroxyethylcellulose, hydroxypropylmethyl cellulose, and carboxymethyl cellulose;

(c) one or more organic solvents, each of which has a boiling point atatmospheric pressure of greater than or equal to 90° C. and up to butless than 500° C., wherein the total Hansen parameter (δ_(T) ^(Polymer))of each of the one or more polymers is less than or equal to the totalHansen parameter (δ_(T) ^(Solvent)) of each of the one or more organicsolvents;

(d) a nitrogenous base having a pKa in acetonitrile of at least 15 andup to and including 25 at 25° C.; and

(e) ascorbic acid, to form a premix solution;

B) maintaining the premix solution at room temperature or heating thepremix solution to a temperature of at least 40° C.;

C) while keeping the premix solution at room temperature or at thetemperature of at least 40° C., adding a solution of either (b)reducible silver ions or (b′) reducible copper ions, in one or more (c)organic solvents to provide an amount of the (b) reducible silver ionsor (b′) reducible copper ions, respectively, in the premix solution thatis equimolar or less in relation to the (d) nitrogenous base, and aweight ratio of the (b) reducible silver ions or (b′) reducible copperions to the (a) one or more polymers of at least 5:1 and up to andincluding 50:1,

to form either a silver nanoparticle composite or a copper nanoparticlecomposite, respectively;

wherein the (e) ascorbic acid is provided in a molar amount of at least0.01:1 relative to either the (b) reducible silver ions or (b′)reducible copper ions, respectively, and

the (d) nitrogenous base is provided in a molar amount of at least 1:1to and including 3:1 relative either the (b) reducible silver ions or(b′) reducible copper ions, respectively,

D) after cooling, isolating the silver nanoparticle composite or thecopper nanoparticle composite; and

E) re-dispersing the silver nanoparticle composite or the coppernanoparticle composite in the same or different (c) one or more organicsolvents used in A), to provide either a non-aqueous silver-containingdispersion or a non-aqueous copper-containing dispersion, comprising thesilver nanoparticle composite or the copper nanoparticle composite,respectively.

2. The method of embodiment 1, further comprising:

disposing either the non-aqueous silver-containing dispersion or thenon-aqueous copper-containing dispersion onto a substrate to form asilver nanoparticle composite composition or copper nanoparticlecomposite composition, respectively, and

removing the same or different (c) one or more organic solvents.

3. The method of embodiment 2, comprising disposing either thenon-aqueous silver-containing dispersion or the non-aqueouscopper-containing dispersion onto the substrate in a patternwise manner.

4. The method of embodiment 2 or 3, wherein the substrate has a firstsupporting side and a second opposing supporting side, and the methodcomprises disposing either the non-aqueous silver-containing dispersionor the non-aqueous copper-containing dispersion onto the substrate in apatternwise manner to form at least one pattern of either a silvernanoparticle composite composition or a copper nanoparticle compositecomposition, respectively, on at least the first supporting side.

5. The method of embodiment 4, wherein the substrate is a continuouspolymeric film, and the method comprises disposing either thenon-aqueous silver-containing dispersion or the non-aqueouscopper-containing dispersion onto the substrate in a manner to formmultiple patterns of either a silver nanoparticle composite compositionor a copper nanoparticle composite composition, respectively, on atleast the first supporting side.

6. The method of embodiment 5, further comprising disposing either thenon-aqueous silver-containing dispersion or the non-aqueouscopper-containing dispersion onto the substrate in a manner to formmultiple patterns of either the non-aqueous silver-containing dispersionor the non-aqueous copper-containing dispersion on the second opposingsupporting side.

7. The method of any of embodiments 2 to 6, wherein the substrate is acontinuous web that is unrolled from a supply roll and is taken up usinga take-up roll, and the method is carried out in a continuousroll-to-roll manner.

8. The method of any of embodiments 1 to 7, wherein silver is present inthe non-aqueous silver-containing dispersion at a weight ratio to the(a) one or more polymers of at least 5:1 and up to and including 20:1,and copper is present in the non-aqueous copper-containing dispersion ata weight ratio to the (a) one or more polymers of at least 5:1 and up toand including 20:1.

9. The method of any of embodiments 1 to 8, wherein the (c) one or moreorganic solvents is one or more hydroxylic organic solvents each havingan α-hydrogen atom and is chosen from the group consisting of ethanol,n-propanol, n-butanol, n-pentanol, n-hexanol, n-octanol,2-ethyl-1-hexanol, n-decanol, ethylene glycol, propylene glycol, benzylalcohol, isobutyl alcohol, isoamyl alcohol, secondary butylcarbinol,isopropyl alcohol, secondary butyl alcohol, secondary amyl alcohol,diethyl carbinol, methyl isobutyl carbinol, methyl-3-heptanal,diisobutyl carbinol, dodecanol-Z, methyl allyl carbinol, cyclohexanol,methyl cyclohexyl carbinol, phenyl methyl carbinol, 2-methoxyethanol,2-ethoxyethanol, diethylene glycol monoethyl ether, methoxy isopropanol,and a combination thereof.

10. The method of any of embodiments 1 to 9, wherein the (d) nitrogenousbase is selected from the group consisting of1,4-diazabicyclo[2.2.2]octane (DABCO), cyclohexylamine, piperidine,N-methyl pipperidine, N-methyl-3-piperidinol, ethanol amine,2-(ethylamino)ethanol, 2-(methylamino)ethanol, 2-(butylamino)ethanol,methyldiethanolamine (MDEA), diethanolamine (DEA), diglycolamine (DGA),diethylaminoethanol (DEAE), substituted or unsubstituted non-polymericpyridine, picolines, lutidines, quinoline, purine, isoquinoline,imidazole, benzimidazole, benzthiazole, thiazole, oxazole, benzoxazole,4,4′-bipyridine, pyrazine, triazine, pyrimidine, nicotinic acid,isonicotinic acid compounds, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU),and a combination thereof.

11. The method of any of embodiments 1 to 10, wherein the (a) one ormore polymers are one or more of carboxymethyl cellulose, celluloseacetate butyrate, ethyl cellulose, cellulose acetate, and celluloseacetate propionate.

12. The method of any of embodiments 1 to 11, wherein either thenon-aqueous silver-containing dispersion or the non-aqueouscopper-containing dispersion has a viscosity of at least 1 centipoise(0.001 Pascal sec) and up to and including 5000 centipoise (5 Pascalsec) at 25° C.

13. The method of any of embodiments 1 to 12, wherein the ascorbic acidis provided in a molar amount of at least 0.02:1 to and including 2:1,relative to either the (b) reducible silver ions or (b′) reduciblecopper ions, respectively.

14. The method of any of embodiments 1 to 13, wherein (b) reduciblesilver ions are added to the premix solution and not (b′) reduciblecopper ions.

15. An article provided by the method of any of embodiments 2 to 14,wherein either the silver nanoparticle composite composition or thecopper nanoparticle composite composition, is disposed in dry form on afirst supporting side of the substrate, wherein:

the silver nanoparticle composite composition comprises silvernanoparticles, and both the (a) one or more polymers and (e) ascorbicacid adsorbed on the silver nanoparticles; and

the copper nanoparticle composite composition comprises coppernanoparticles, and both the (a) one or more polymers and (e) ascorbicacid adsorbed on the copper nanoparticles.

16. The article of embodiment 15, wherein the (a) one or more polymersis one or more of carboxymethyl cellulose, cellulose acetate butyrate,ethyl cellulose, cellulose acetate, and cellulose acetate propionate.

17. The article of embodiment 15 or 16, wherein either the silvernanoparticle composite composition or the copper nanoparticle compositecomposition, is disposed in dry pattern on a first supporting side ofthe substrate.

18. The article of any of embodiments 15 to 17, further comprisingeither a silver nanoparticle composite composition or a coppernanoparticle composite composition, disposed in dry form on a secondopposing supporting side of the substrate.

19. The article of any of embodiments 15 to 18, wherein the substrate isa continuous polymeric web.

20. The article of any of embodiments 15 to 19, wherein the substrate iscomposed of an organic polymer, fabric, or glass.

The following Examples are provided to illustrate the practice of thisinvention and are not meant to be limiting in any manner.

Invention Example 1: Preparation of Non-Aqueous Dispersion of SilverNanoparticle-Ethyl Cellulose Composite Using Ascorbic Acid andNitrogenous Base at 40° C.

In a two-necked round bottomed flask, ethyl cellulose (0.42 g, ethoxylcontent 48%) was dissolved in 2-methoxyethanol (37.0 g) by stirring at40° C. for 30 minutes. Ascorbic acid (9.127 g, 51.8 mmol) and thenitrogenous base 2-methylaminoethanol (7.79 g, 104 mmol) were then addedto the flask. Stirring was continued until all ascorbic acid dissolvedto form a premix solution. A solution of silver nitrate (8.8 g) in2-methoxyethanol (105 g, 8.3 weight %) was added over two hours with theaid of a peristaltic pump; and the resulting reaction mixture wasstirred for an additional thirty minutes and then poured into 800 ml ofwater. The black precipitate thus formed was filtered (Whatman GF/F, 0.7μm), washed with water, and dried to provide a black solid of the silvernanoparticle composite. ZEN Particle Sizing of another aliquot of theslurry prior to precipitation showed silver nanoparticle compositeparticles with average size of 240 nm (see FIG. 1).

The silver content of the resulting silver nanoparticle-ethyl cellulosecomposite was measured using thermogravimetric analysis (TGA) using asmall amount of the obtained black solid that was scanned attemperatures ranging from room temperature to 700° C. in air. Organicmaterials are burnt and removed during the TGA scan. The residual weightat 700° C. corresponded to the amount of silver in the solid sample.Consistent with the starting weight ratios, the gray solid comprised 95%by weight of silver and 5% weight total of ethyl cellulose and otherorganics.

The dried silver nanoparticle composite was re-dispersed in1-methoxy-2-propanol (at 40 weight %) by using a high shear mixer(Silverson L4R) to obtain a printable non-aqueous silver-containingdispersion (or “ink”). An electrically-conductive silver-containingpattern (see FIG. 2) was formed in an article using this non-aqueoussilver nanoparticle-containing composition on a poly(ethyleneterephthalate) (PET) film substrate using a flexographic test printerIGT F1 and flexographic printing members obtained from commerciallyavailable Kodak Flexcel NX photopolymer plates that had been imagedusing a mask that was written using the Kodak Square Spot lasertechnology at a resolution of 12,800 dpi.

Invention Example 2: Preparation of Non-Aqueous Dispersion of SilverNanoparticle-Ethyl Cellulose Composite Using Ascorbic Acid andNitrogenous Base at 40° C.

In a two-necked round bottomed flask, under a nitrogen atmosphere, ethylcellulose (0.42 g, ethoxyl content 48%) was dissolved in2-methoxyethanol (37.0 g) by stirring at 40° C. for 30 minutes. Ascorbicacid (9.127 g, 51.8 mmol) and the nitrogenous base 2-methylaminoethanol(7.79 g, 104 mmol) were then added to the flask. Stirring was continueduntil all ascorbic acid dissolved to form a premix solution. A solutionof silver nitrate (8.8 g) in 2-methoxyethanol (105 g, 8.3 weight %) wasadded over two hours with the aid of a peristaltic pump; and theresulting reaction mixture was stirred for an additional thirty minutes.The black solid was filtered (Whatman GF/F, 0.7 μm), washed with2-methoxyethanol, and dried to provide a black solid of the silvernanoparticle.

The dried silver nanoparticle ethyl cellulose composite was re-dispersedin 1-methoxy-2-propanol (at 40 weight %) by adding appropriate amount ofethyl cellulose and mixing. Thus, to a solution of ethyl cellulose (0.11g) in 1-methoxy-2-propanol (5 ml), the particles of silver nanoparticleethyl cellulose composite (2 g) prepared above were added and mixed byusing a high shear mixer (Silverson L4R) to obtain a printablenon-aqueous silver-containing dispersion (or “ink”). The weight ratio ofsilver to ethyl cellulose in this ink was 95:5. ZEN Particle Sizing ofanother aliquot of this slurry showed silver nanoparticle ethylcellulose composite particles with average size of 200 nm.

An electrically-conductive silver-containing pattern (see image in FIG.2) was formed in an article using this non-aqueous silvernanoparticle-containing composition on a poly(ethylene terephthalate)(PET) film substrate using a flexographic test printer IGT F1 andflexographic printing members obtained from commercially available KodakFlexcel NX photopolymer plates that had been imaged using a mask thatwas written using the Kodak Square Spot laser technology at a resolutionof 12,800 dpi.

Invention Example 3: Preparation of Non-Aqueous Dispersion of CopperNanoparticle-Cellulose Acetate Using Ascorbic Acid and Nitrogenous Baseat 40° C.

In a two-necked round bottomed flask, cellulose acetate (0.096 g) wasdissolved in 2-methoxyethanol (20.0 g) by stirring at 65° C. for 30minutes. Ascorbic acid (4.82 g, 27.3 mmol) and the nitrogenous base2-butylaminoethanol (3.2 g, 27.3 mmol) were then added to the flask.Stirring was continued until all ascorbic acid dissolved to form apremix solution. A solution of cupric nitrate (3.2 g, 13.6 mmol) in2-methoxyethanol (9 g) was added slowly with the aid of an additionfunnel, and the resulting reaction mixture was stirred for an additional60 minutes. The reaction mixture was poured into 200 ml of water and thereddish precipitate thus formed was filtered and dried to provide acopper nanoparticle composite. ZEN Particle Sizing of another slurryprior to precipitation showed copper nanoparticle composite particleswith average size of 290 nm (see FIG. 3). Formation of coppernanoparticle cellulose acetate composite particles was confirmed bycharacteristic X-ray diffraction (FIG. 4).

Invention Example 4: Preparation of Non-Aqueous Dispersion of SilverNanoparticle-Ethyl Cellulose Using Ascorbic Acid and Nitrogenous Base at40° C.

In this example, the presence of ascorbic acid adsorbed on silvernanoparticles is established.

Ethyl Cellulose (0.712 g) was placed into a 1 liter, 3-neck round bottomflask and dissolved in 2-methoxyethanol (100 g) at 40° C. using amagnetic stir-bar. The temperature was maintained using an oil bath.Ascorbic acid (19.16 g, 0.109 moles) and 2-(methylamino)ethanolnitrogenous base (16.34 g, 0.218 moles) were added and the resultingmixture was stirred until all solids dissolved. Separately, silvernitrate (17.6 g, 0.104 moles) was dissolved in 2-methoxyethanol (200 g)using ultrasonication and then transferred to a dropping funnel where itwas added dropwise to the ethyl cellulose containing solution over 40minutes. A black precipitate formed immediately upon this addition andonce the addition was complete, stirring was continued for an additional20 minutes. The reaction flask removed from heat and while it was stillwarm, a black solid was collected using vacuum filtration (Büchnerfunnel, Whatman 2 filter paper).

The obtained silver nanoparticle composite was thoroughly washed with2-methoxyethanol (400 ml) and methanol (500 ml) to remove ethylcellulose and the solid material was analyzed by TGA-FTIR using a Q50Thermo Gravimetric Analyzer coupled to a Digilab Excalibur FTIR. Themeasurements were performed over the temperature range of roomtemperature to about 700° C. using a ramp protocol of 10° C./min to 125°C. (isotherm 15 minutes), 10° C./min to 250° C. (isotherm 15 minutes),and 20° C./minute to 700° C. Sample weight was 47 mg. For comparison,TGA-IR measurements were also performed on a sample of ascorbic acidusing a ramp protocol of 20° C./min over the same temperature range. Forall samples, a purge of N₂ gas, at a rate of 10 cc/min, was used tosweep the evolved gases through the transfer line and the infrared (IR)gas cell, both heated at a constant temperature of 240° C. Sixteen IRspectra (interferograms) of the evolved gases, at 4 cm-1 resolution,were co-added at approximately 10 second intervals. A TE-TGS detectorwas used for IR detection.

FIGS. 5 and 6 show the TGA and FTIR data, respectively, for the TGA-FTIRmeasurement of the sample. The data show three weight losstransitions: 1) 2.76%, room temperature to 125° C., due mostly to1-methoxy 2-propanol, with CO₂ and H₂O; 2) 2.53%, ˜140° C. to 250° C.,due to CO₂ and trace levels of CO and H₂O; and 3) ˜1.1%, 250° C. to 700°C., due to CO₂ and trace levels of CO, H₂O, and organics.

These two CO₂ weight loss transitions are consistent with thedecomposition of ascorbic acid. As seen in FIG. 7, ascorbic acid beganto decompose with the evolution of CO₂ and H₂O at ˜208° C. This wasfollowed by a second loss of CO₂ beginning at ˜275° C. (trace levels ofCO and organics were also seen). The large loss of CO₂ suggests adecarboxylation mechanism for decomposition. The difference in the onsetto decomposition temperatures (140° C. vs. 208° C.) between the twosilver samples and the ascorbic acid suggests a chemical associationbetween the silver and the ascorbic acid, with the latter possiblyexisting in an ionic form. The lack of substantial levels of water inthe initial weight loss transition (140° C.) of the silver materials,appears to support this belief.

Invention Example 5: Preparation of Non-Aqueous Dispersion of SilverNanoparticle-Ethyl Cellulose Composite Using Small Concentration ofAscorbic Acid and Nitrogenous Base at 80° C.

In a two-necked round bottomed flask, under a nitrogen atmosphere, ethylcellulose (0.42 g, ethoxyl content 48%) was dissolved in2-methoxyethanol (37.0 g) by stirring at 80° C. for 30 minutes. Ascorbicacid (0.110 g, 0.625 mmol) and the nitrogenous base 2-methylaminoethanol(7.79 g, 104 mmol) were then added to the flask. Stirring was continueduntil all ascorbic acid dissolved to form a premix solution. A solutionof silver nitrate (8.8 g, 51.8 mmol) in 2-methoxyethanol (105 g, 8.3weight %) was added over two hours with the aid of a peristaltic pump;and the resulting reaction mixture was stirred for an additional thirtyminutes. The reaction mixture was poured into water (800 ml) and greysolid was filtered (Whatman GF/F, 0.7 μm), washed with water, and driedto provide a gray solid of the silver nanoparticle composite.

The dried silver nanoparticle ethyl cellulose composite was re-dispersedin 1-methoxy-2-propanol (at 40 weight %). Thus, in 1-methoxy-2-propanol(5 ml), the particles of silver nanoparticle ethyl cellulose composite(2 g), prepared above, were added and mixed by using a high shear mixer(Silverson L4R) to obtain a printable non-aqueous silver-containingdispersion (or “ink”). The weight ratio of silver to ethyl cellulose inthis ink was 95:5 (obtained by TGA). ZEN Particle Sizing of anotheraliquot of this slurry showed silver nanoparticle ethyl cellulosecomposite particles with average size of 200 nm.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

1. A method comprising, in sequence: A) mixing: (a) one or more polymersselected from one or more of cellulose acetate, cellulose acetatephthalate, cellulose acetate butyrate, cellulose acetate propionate,cellulose acetate trimellitate, hydroxypropylmethyl cellulose phthalate,methyl cellulose, ethyl cellulose, hydroxyethyl cellulose,hydroxypropylmethyl cellulose, and carboxymethyl cellulose; (c) one ormore organic solvents, each of which has a boiling point at atmosphericpressure of greater than or equal to 90° C. and up to but less than 500°C., wherein the total Hansen parameter (δ_(T) ^(polymer)) of each of theone or more polymers is less than or equal to the total Hansen parameter(δ_(T) ^(Solvent)) of each of the one or more organic solvents; (d) anitrogenous base having a pKa in acetonitrile of at least 15 and up toand including 25 at 25° C.; and (e) ascorbic acid, to form a premixsolution; B) maintaining the premix solution at room temperature orheating the premix solution to a temperature of at least 40° C.; C)while keeping the premix solution at room temperature or at thetemperature of at least 40° C., adding a solution of either (b)reducible silver ions or (b′) reducible copper ions, in one or more (c)organic solvents to provide an amount of the (b) reducible silver ionsor (b′) reducible copper ions, respectively, in the premix solution thatis equimolar or less in relation to the (d) nitrogenous base, and aweight ratio of the (b) reducible silver ions or (b′) reducible copperions to the (a) one or more polymers of at least 5:1 and up to andincluding 50:1, to form either a silver nanoparticle composite or acopper nanoparticle composite, respectively; wherein the (e) ascorbicacid is provided in a molar amount of at least 0.01:1 relative to eitherthe (b) reducible silver ions or (b′) reducible copper ions,respectively, and the (d) nitrogenous base is provided in a molar amountof at least 1:1 to and including 3:1 relative either the (b) reduciblesilver ions or (b′) reducible copper ions, respectively, D) aftercooling, isolating the silver nanoparticle composite or the coppernanoparticle composite; and E) re-dispersing the silver nanoparticlecomposite or the copper nanoparticle composite in the same or different(c) one or more organic solvents used in A), to provide either anon-aqueous silver-containing dispersion or a non-aqueouscopper-containing dispersion, comprising the silver nanoparticlecomposite or the copper nanoparticle composite, respectively.
 2. Themethod of claim 1, further comprising: disposing either the non-aqueoussilver-containing dispersion or the non-aqueous copper-containingdispersion onto a substrate to form a silver nanoparticle compositecomposition or copper nanoparticle composite composition, respectively,and removing the same or different (c) one or more organic solvents. 3.The method of claim 2, comprising disposing either the non-aqueoussilver-containing dispersion or the non-aqueous copper-containingdispersion onto the substrate in a patternwise manner.
 4. The method ofclaim 2, wherein the substrate has a first supporting side and a secondopposing supporting side, and the method comprises disposing either thenon-aqueous silver-containing dispersion or the non-aqueouscopper-containing dispersion onto the substrate in a patternwise mannerto form at least one pattern of either a silver nanoparticle compositecomposition or a copper nanoparticle composite composition,respectively, on at least the first supporting side.
 5. The method ofclaim 4, wherein the substrate is a continuous polymeric film, and themethod comprises disposing either the non-aqueous silver-containingdispersion or the non-aqueous copper-containing dispersion onto thesubstrate in a manner to form multiple patterns of either a silvernanoparticle composite composition or a copper nanoparticle compositecomposition, respectively, on at least the first supporting side.
 6. Themethod of claim 5, further comprising disposing either the non-aqueoussilver-containing dispersion or the non-aqueous copper-containingdispersion onto the substrate in a manner to form multiple patterns ofeither the non-aqueous silver-containing dispersion or the non-aqueouscopper-containing dispersion on the second opposing supporting side. 7.The method of claim 2, wherein the substrate is a continuous web that isunrolled from a supply roll and is taken up using a take-up roll, andthe method is carried out in a continuous roll-to-roll manner.
 8. Themethod of claim 1, wherein silver is present in the non-aqueoussilver-containing dispersion at a weight ratio to the (a) one or morepolymers of at least 5:1 and up to and including 20:1, and copper ispresent in the non-aqueous copper-containing dispersion at a weightratio to the (a) one or more polymers of at least 5:1 and up to andincluding 20:1.
 9. The method of claim 1, wherein the (c) one or moreorganic solvents is one or more hydroxylic organic solvents each havingan α-hydrogen atom and is chosen from the group consisting of ethanol,n-propanol, n-butanol, n-pentanol, n-hexanol, n-octanol,2-ethyl-1-hexanol, n-decanol, ethylene glycol, propylene glycol, benzylalcohol, isobutyl alcohol, isoamyl alcohol, secondary butylcarbinol,isopropyl alcohol, secondary butyl alcohol, secondary amyl alcohol,diethyl carbinol, methyl isobutyl carbinol, methyl-3-heptanol,diisobutyl carbinol, dodecanol-Z, methyl allyl carbinol, cyclohexanol,methyl cyclohexyl carbinol, phenyl methyl carbinol, 2-methoxyethanol,2-ethoxyethanol, diethylene glycol monoethyl ether, methoxy isopropanol,and a combination thereof.
 10. The method of claim 1, wherein the (d)nitrogenous base is selected from the group consisting of1,4-diazabicyclo[2.2.2]octane (DABCO), cyclohexylamine, piperidine,N-methyl pipperidine, N-methyl-3-piperidinol, ethanol amine,2-(ethylamino)ethanol, 2-(methylamino)ethanol, 2-(butylamino)ethanol,methyldiethanolamine (MDEA), diethanolamine (DEA), diglycolamine (DGA),diethylaminoethanol (DEAE), substituted or unsubstituted non-polymericpyridine, picolines, lutidines, quinoline, purine, isoquinoline,imidazole, benzimidazole, benzthiazole, thiazole, oxazole, benzoxazole,4,4′-bipyridine, pyrazine, triazine, pyrimidine, nicotinic acid,isonicotinic acid compounds, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU),and a combination thereof.
 11. The method of claim 1, wherein the (a)one or more polymers are one or more of carboxymethyl cellulose,cellulose acetate butyrate, ethyl cellulose, cellulose acetate, andcellulose acetate propionate.
 12. The method of claim 1, wherein eitherthe non-aqueous silver-containing dispersion or the non-aqueouscopper-containing dispersion has a viscosity of at least 1 centipoise(0.001 Pascal sec) and up to and including 5000 centipoise (5 Pascalsec) at 25° C.
 13. The method of claim 1, wherein the (e) ascorbic acidis provided in a molar amount of at least 0.02:1 to and including 2:1,relative to either the (b) reducible silver ions or (b′) reduciblecopper ions, respectively.
 14. The method of claim 1, wherein (b)reducible silver ions are added to the premix solution and not (b′)reducible copper ions.
 15. An article provided by the method of claim 2,wherein either the silver nanoparticle composite composition or thecopper nanoparticle composite composition, is disposed in dry form on afirst supporting side of the substrate, wherein: the silver nanoparticlecomposite composition comprises silver nanoparticles, and both the (a)one or more polymers and (e) ascorbic acid adsorbed on the silvernanoparticles; and the copper nanoparticle composite compositioncomprises copper nanoparticles, and both the (a) one or more polymersand (e) ascorbic acid adsorbed on the copper nanoparticles.
 16. Thearticle of claim 15, wherein the (a) one or more polymers is one or moreof carboxymethyl cellulose, cellulose acetate butyrate, ethyl cellulose,cellulose acetate, and cellulose acetate propionate.
 17. The article ofclaim 15, wherein either the silver nanoparticle composite compositionor the copper nanoparticle composite composition, is disposed in drypattern on a first supporting side of the substrate.
 18. The article ofclaim 15, further comprising either a silver nanoparticle compositecomposition or a copper nanoparticle composite composition, disposed indry form on a second opposing supporting side of the substrate.
 19. Thearticle of claim 15, wherein the substrate is a continuous polymericweb.
 20. The article of claim 15, wherein the substrate is composed ofan organic polymer, fabric, or glass.